A few weeks ago I had a discussion with some people on Twitter as to why there was a limit of 99 friends on Twitter. They thought it was a pretty easy change to make but I argued that with such a large system you had to consider the extra storage,bandwidth, and the fact that someone probably hard coded the number of friends into a game. It turns out I was right about the hard coded limit (+100 internet points to me) as Aaron Greenberg mentioned in this interview
with 1up yesterday. He doesn't out the developer who did this but once again backwards compatibility comes back to haunt Microsoft. He does point out that the average Live user only has about 30 friends though so I can't imagine this is too high of a priority.