Sega is overall pretty evenly spread over the different platforms.
With the Sega Ages titles, however, their just trying to make some quick cash by sprucing up some classic titles. While I won't be going out to buy a PS2 anytime soon, I'm glad they're doing it. If they were only released on the GC or XBox, they might not sell many copies and would probably end up canceling the series.
Hopefully the Ages series will sell well and Sega will produce a large library of games -- and maybe even port the most popular ones to other systems.