Mac is based on Unix, which is what Linux is based off of. It's generally a stable system, and can call data quickly. Therefore, it can access smaller amounts of RAM quickly, and use the Hard Drive with low latency.
It also has good low-priced video editing.
Windows Vista has no widely-distributed mainframe, and nobody's really sure how it works or how it processes data. It needs more RAM than XP and 7, which will be released later this year or so, and it calls that data slower than 7. Vista also uses a large amount of space for logs, which takes a good portion of even my 4GB RAM to write.
I'm not saying all of Windows is bad at video editing. Windows 7 might get my attention enough to switch back over completely, because at this time, I have both operating systems, and two laptops.