Well let me introduce you to
GameSpy Arcade (on the PC) as one example. It featured system-wide messaging, voice-chat, an account system as well as server browsing all the way back in early 2000, long before the 360 released.
Achievements were done in some games before (E-Motion on the Amiga for one), just not in a system-wide implementation like the 360.
Aside from the few frivolous improvements you've mentioned, you're essentially paying $60 for a P2P online service. But this isn't the place to be talking about my gripes with online gaming on consoles. It's just that the majority of these things aren't really revolutionary when you consider the fact that PC gaming had most of this long before the 360.