XSI is gaining massive ground in movie production, mainly because it's new features actually have a practical application in the movie business

Take version 3 for example, it has massive improvements to subd's, it's hair system is fantastic and crowd simulation which has the potential to rival Massive

Where as Maya Unlimited (apparently XSI Advance's main rival), its only major new feature is Fluid Effects. Which isn't compatible with either MR or PRman (the 2 main renderers in the movie business) and I can't imagine many movies need Fluid Effects anyway