It's not the hardware makers having third party problems, it's the third parties having hardware-maker problems.

Sony and Microsoft priced themselves out of the market...possibly because they had no choice if they wanted to offer a level of hardware improvement that was acceptable to traditional gamers.
Nintendo came up with a new product that leaves a lot of the traditional market angry or at least dumbfounded, but that is cheap enough to grab up a lot of the traditional market plus some new markets.
Most third parties banked on the traditional consoles because they could quantify the audience. Many PS3 projects were probably started 2-3 years ago when companies still thought PS3 would dominate the market. And why wouldn't you think that? Until people saw the Wii line-ups at E3, and heard Sony's ridiculous price, there was no telling things would turn out this way. Even after that, many people were still skeptical: who would have predicted that Wii would still be sold out in many places even 8 months after launch? Even huge proponents of the blue ocean / disruption business plan figured it would take about a year for Wii to catch on.
So what we have is a situation where a lot of third parties are very invested in a big loser - PS3 - and most of them are way behind the curve on the big winner - Wii. In fact many of them
still aren't sure if Wii is the real deal. It's not surprising, then, that third party support is all over the place.
Of course I'm ignoring 360, which actually has quite good third party support, it's just focused on a narrow demographic. That's not a huge surprise, the original Xbox had the same problem (even worse), but I don't think people realized it as much until 360 had the first-mover advantage and had trouble selling systems.