I havent noticed a drop off in sys link games. Maybe thats because I adhere too the same types of games and they still all offer sys link.
CoD 2, quake 4, pgr 3, hell even quake 2 has it, lol. I do wish CoD 2 offered Coop, be it Lan or Live, or both. Ahh well.
None of the games I fell inlove with at xbox launch and sys link, lost that feature over the years, be it a racer, fps, whatever. I never owned a Burnout, always rented them. Never had it long enough to care about sys link, also none of my friends had them so there was noone to lan with anyways.
Im still sad about Brute Force