It's funny hearing a lot of the conjecture about HL2 on the Xbox. I've heard rumors saying "Oh yeah, there'll be support for mods on Xbox Live, and lots of downloadable content from other users!"
When you also hear stuff regarding other games not ported to Xbox stating "We didn't want to port this online game because of Microsoft's strict control of Xbox live, where everything needs to be approved by Microsoft before it's available for downloadable content on Xbox Live."
I agree that the game was good in Story Mode, but the thing that kept it alive in online playing was the extreme number of mods available. I mean, it bred 2 essentially new games using the same engine and simply using mods on the main game, not to mention the countless more amateur mods that made it online. The mods were out almost as soon as the game was released, and although were more basic than the mods that eventually came out, they really gave people more reason to play online instead of some other game.
So I really don't see how it's going to be that different on Xbox Live compared to, well, any other FPS on Xbox Live right now. You can't really have a mod community on Xbox Live, as you can't transfer content between users and you can't load up your own server or upload modded content for online play without Microsoft OK'ing it (which you know they won't do unless it's from the developer). Everyone who wants to play HL2 will get it for PC, instead of for the console, as they know they'll end up with a lot more content to download AND won't have to pay to play.