An article by David Nagel explains why Adobe found the PC "Preferred", even when comparing against a dual-processor Macintosh.

The complaint is that it is Adobe's flawed After Effects software that is at the root of the problems. However, it isn't the usual "the software just stinks" complaint, it's a complaint backed by benchmarks that indicate that After Effects sees very little benefit from dual processor machines, unlike its competitors Final Cut Pro (Apple), and Combustion (Discrete), which see 160-175% increase in speed by adding more processors.

Food for thought, and an explanation why the digital video folks at Adobe might "prefer" PC's... that and the fact that Adobe is doing a joint marketing campaign to sell Dells... but that couldn't have anything to do with it, could it?