You need to more clearly define what you mean by "HD Audio". Audio has come very far on consoles, just no one is paying attention. Its way beyond what it was back in the 1999 aureal days.
I've had a 5.1 system for years hooked up to my 360/ps3, and I've found the positioning to be nothing short of perfect, especially with FPS games. I could absolutely close my eyes and pinpoint directions...I simply do not hear the whole center channel effect youre talking about.
Perhaps many of you need to properly set up and tune your systems or place your speakers?
Also, dont overstate what kind of positioning you could actually accomplish with only 5 speakers - it is going to be virtually impossible to localize sounds on the screen itself, even if its a huge screen. You just cant pull that off with three front speakers. If it were so easy to localize sounds by blending speakers, you wouldn't need a center channel at all.
And then there's a number of challenges on top of that...a screen is a much easier to define space...the left side of the screen will always be just that. But the left speaker could be bordering the screen, or way out to the left...and there's no way for the system or game to know where exactly. So positioning a sound that precisely, especially by blending channels, is pretty much out of the question. Surround could be to the side or behind. An then there's room acoustics on top of that, which can completely change the game, especially since no two rooms are alike.
And even then, there's no clearly defined spec for placing speakers. Ideally, for 5.1 you'd want the speakers in a ring around you, with the fronts 30 degrees to the side, and the surrounds 45 degrees behind. You'd absolutely need to follow your recievers auto calibration with the included mic, or get out an spl meter to balance them, and you'd need to make sure there's no egregious acoustical issues.