Don't disregard the major impact that PR and promotion plays in CGI in the film industry. Maya, in particular, has been relentless in pushing its product in the film industry, and has had a great deal of sucess, largely it seems at the expense of SI. For some reason, discreet never made that push. It did for a short time back in 1997 or so, when Lost in Space came out, but then they just gave up.
Also, don't ignore the "snob" factor. High-end effects shops were born and raised on SI and PA, which were the ultra-high end at the time, and have always looked down their noses at max, LW, and the other less expensive "upstarts." I'm not sitting in judgment of anyone here, and I don't mean to offend anyone, but come on -- you know it's true! In addition, these high-end shops face the very real business challenge of getting people to pay big money for their work. You get to justify big fees in part by using big ticket software and hardware.
You also try to justify big fees by developing custom software, shaders, and tools for a project, even if something off the rack may be just as good. Come on now, guys, how many times have you read an article on the making of the CG effects in a particular movie, and the high-end shop responsible for the work was waxing eloquent about all the custom software and tools they developed, and you said to yourself: "Why did they spend all that time and money developing a plugin to do that, when so-and-so sells a plugin for max that does esentially the same thing for a few hundred bucks?"
Eric Twiste