That's another part about it, but on the other hand:
1. What if the live-action movie was based on the anime, not the games? Live-action anything based on anime generally tend to turn out well. (That is, even if it's not a mainstream hit, it tends to be a cult hit.)
2. It usually depends on who does it. Americans handling the production of an anime movie, yes, I wouldn't be surprised if it sucks (given what American writers have done with the live-action concept already -- *motions to the aforementioned Pokemon musical*). The Japanese doing it, however, is a different story. Maybe it has something to do with Japanese cinema in general (because I have yet to see a Japanese movie that didn't outright bite), but when the Japanese take an anime series and decide, "Hey! Let's make a live-action series/movie out of this!," it generally gathers a nice-sized fan following for a good reason. (Take Super Mario Bros and compare it to, as mentioned before, PGSM. Of course, what failed with SMB was that it deviated so much from the actual franchise to the point where even Mario was only vaguely recognizable, but that's Hollywood "experimenting" for you.)