That's right, everybody seems to be playing the same game(s). Every time a big game is released, that one game is in the now-playing display for just about everybody.
Oblivion? In the list.
Saints Row? Fairly popular around release.
Gears of War? Currently all over the list.
Madden? Nah. I don't roll with that crew.

The thing I always notice when this effect occurs . . . I'm not playing that game.

Caro and I gunned down alien armies in Contra.
Peldon(x2) and I rolled through the mean streets of Need for Speed Carbon.
I've sent invites to others appearing on the list and in the GS communities, but it just hasn't worked out thus far. Maybe I am just a third . . . er, fifth wheel, but other games are out there. When I was racking up mad points in Lego Star Wars II, I didn't see too many people with it in their trays. Perhaps my tastes are just different.

I like the back catalogue and the proven successes. . . with a few exceptions.

When I am not on I am actually on, but playing Oblivion. I haven't used the Appear Offline function at all until this last week. Turning off all of the notifications and appearing offline has ensured a deep, immersive experience for Oblivion. The only drawback has been the fact that I can't play it with anyone else!

. . . and really these days only multiplayer is really of interest to me. That feature gives the game legs.