When you are rendering 3d video with effects and multiple layers, etc., you need as much power as you can buy. For his senior project (5 minute video), one of my friends had to use 15 dual XEON computers to render overnight. Sure, you can buy 8.5 computers instead of one, but what if you only have room for 8 computers, and you need eight guys working on them, and you cannot afford to wait as long as the speed/processing power of a single computer would allow per workstation? You buy as much as you can afford/computer.
Getting one such workstation to edit homemovies and manage your iPod would be overkill. If you are doing hardcore game design and or 3d graphics, or even 2d video sometimes, if you will make your money back, go for the big guns. Very often such businesses lease their computer equipment anyways. Even if they buy, they end up getting special pricing, so they wouldn't pay a full $17k per computer.