Just as a note on Rob’s co
Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Editing › Why is Final Cut so popular? › Just as a note on Rob’s co

Just as a note on Rob’s comment above, my understanding from the dealers and online guru’s – if you don’t physically break something (like drop a coin onto the motherboard with the power on), adding RAM and/or internal hard drives does not void the Apple warranty.
As to some of the previous comments – I’ve used both Mac and PC platforms extensively. I actually do have both on my desk at this moment, with a KVM switch using one monitor, keyboard and (3 button) mouse. I much prefer Mac because I know the machine itself is built to very high standards with usually great parts (there have been exceptions, but for the most part, very good) and software that has a (generally) consistent interface and plays well with the hardware. And, AVCHD issues aside, Macs have always played with PC files much better than PC’s play with Mac (and often PC) files.
I can’t say that for the dozen or so PC’s I’ve used over the years.
If you’re not a “technical person” that has the knowledge to properly build your own machine – and the vast majority of people really don’t – Macs are a better choice.
So for the OP – FCP is so popular because it makes the job of editing reasonably easy for a decent (though not free) cost on a platform that does a very good job with few issues. When you want to get the job done without becoming a “technician” for your computer, Macs generally win, and FCP has been the application of choice.
(BTW – if you’re equipping a medium to large studio, experience has shown that tech support for Macs costs one third that of PC’s. Put that into your Cost of Ownership calculations before your purchase.)
Neil