WARNING: LONG READ.
Why do I think this? It's quite simple, actually, but to understand this we have to look to the past. Note that this has a lot of computer-related lingo, so watch out...
*hops in time-travelling Delorean, sets it to January 2000*
Playstation 2 is the first next-generation console released, and developers flock to it seeing themselves having the success other developers had with the original PlayStation. Developers had a lot of trouble developing for it, since the SDK was unlike any others, and the CPU architecture was not directly related to any other architectures. However, they eventually learnt how to develop for it, since it was the only next-gen console out at the time (excluding the flop/bundle of joy known as DreamCast).
*sets Back to the Future car to Q3/Q4 2001*
So by now, developers have PS2 development down. They are now comfortable with the PS2's SDK, and even though it's difficult to work with, they don't want to change. So now, Microsoft has already announced its' entry into the console market, the Xbox... Which is just a computer with a 733MHz Celeron and an upgraded nVidia GeForce 3. For non-computer-hardware-savvy people, this is basically a run-of-the-mill computer. Hence, any company that had developed games for a PC using the DirectX programming libraries was already at home on the Xbox, and its' SDK.
And then, there's the odd man out... Nintendo's GameCube. It's running on an IBM "Gecko" chip, which is a custom PowerPC chip. PPC is the type of CPU that is used in Apple's Mac (well, until recently, but more on that later). And one thing that's a trade-off when you get a Mac is this: Unfortunately, barely anybody develops Mac games. No game developers have any real experience with the PPC architecture yet. Well, except for one of the major Mac games companies, Bungie... But I think we all know how they turned out. Because of this, even though it had a very easy-to-learn SDK, Nintendo's GCN hasn't really done so well in the third-party department.
*goes back to the present time*
Okay, now we're back in late 2005. So let's go through the systems again, by time of introduction. Microsoft's X360 is, again, a computer, but now resembles a Mac computer more than an x86 computer (anything that runs Windows is an x86 box). It's running on three custom PowerPC variants and an ATi video card based on the R500 core. This situation will be very similar to that of the Playstation 2: The first one out gets the most support. The SDK is reportedly very different from that of the original Xbox. Unlike the PS2 situation, however, the X360's development environment (the program in which code is written and compiled) is based off of Visual Studio 2005, giving it at least some recognizability to PC and Xbox developers. John Carmack, the creator of the Doom series, says that he as a PC developer is extremely satisfied with X360's development environment.
Next up, we have everybody here's favorite future console, Nintendo's Revolution. We don't have much in the way of solid information specifications-wise, but we know this: Nintendo has said that Revolution development will be similar, if not exactly the same as the Gamecube's SDK. We also know that Gamecube games will be playable inside a Revolution. And lastly, we know that IBM will be manufacturing the CPU. From this, I think it is logical to believe that Revolution will feature a processor that is very similar to that of the Gamecube. Meaning that Revolution will most likely have a PowerPC variant at its' heart. We also know that the video card will be using ATi's RN520 core. (ATi bought the company that made the GCN's graphics core, which in turn was made up of a bunch of guys from Silicon Graphics who developed the N64's graphics chip.) Of course, the main thing Revolution has going for it is the controller, but we don't know anything about that yet, excluding the fact that it will be backwards-compatible with the controllers of previous consoles... Meaning that the controller won't require third-party developers to make some cockamaney control scheme for Revolution if they are porting games from X360 or Revolution.
And lastly, the Playstation 3. Ah, Sony, always trying to do some crazy stuff with your hardware. Specifically, this time, with their Cell processor. The Cell CPU is, in a few words, a PPC CPU with seven much less powerful "mini-CPUs" attached to it, each of which can be assigned with a specific task - For instance, calculating physics. In the PC world, programmers have a known grudge against developing for just two CPUs running in tandem (dual-core). Now just imagine how much devs are going to love developing for 8 CPUs. Developers have never liked Sony's SDKs, and the reason they put up with them is because they were the only available way to develop for the only available next-generation console. But that's not all! Sony's making the same mistake Nintendo made in the Nintendo 64 era: Their storage medium is too expensive. Sony is using their Blu-Ray storage medium instead of DVDs, and Blu-Ray is pretty expensive. Also, lastly, Sony hired nVidia to make their RSX graphics chip.
So let's compare the three.
X360:
-SDK: "XNA". Somewhat similar to Xbox/PC development
-CPU: Xenon. Which is just 3 custom PPCs. Architecture is new to Xbox/PC developers. Multi-threading (>1 CPU) is optional, but it's a pain to programmers.
-GPU: ATi R500. ATi is oneo f the big players in the PC graphics industry, and the R500 core is their next big upgrade. Hasn't been unveiled yet.
-Storage: DVD9. More expensive than DVD, much less expensive than Blu-ray.
Revolution
-SDK: "???". Exactly the same as the GameCube.
-CPU: IBM Broadway. It's a PPC, and that's all we know. Meaning it will be familiar to anybody that develops for PPC - which is in all next-gen consoles. We don't know if it'll have more than one core.
-GPU: ATi Hollywood. Uses RN520 core, which will probably be similar to X360's R500.
-Storage: DVD. Cheapest of the three.
PS3:
-SDK: "???". Entirely new. Has a history of being hard to develop for.
-CPU: The Cell. Based on PPC, but will require extremely annoying multi-threaded programs.
-GPU: nVidia RSX. No real details on it yet.
-Storage: Blu-Ray. Expensive but holds more.
So what can we deduct from this? It's quite simple - Revolution and X360 seem to share a lot in common. I would not be surprised if many third-party developers released their games for both X360 and Revolution, since their innards are so similar. And PS3, with such a high learning curve and higher cost, will probably be left in the dust.
Just my two cents.