I often look at the specialist games but then realize that I play 40k so infrequently and I know a bunch of people that play and I don't know anyone that plays Blood Bowl, so I shouldn't buy it. Although...Blood Bowl is a bad example...cuz I did buy it and I still haven't played.
Ok, take out Blood Bowl and replace it with Epic and then it will be valid.
I also think it's because some of the old models are really cool. I have a 40k Leman Russ (the primarch, not the tank), but how would I ever use him. He's so badass though!