With Avid, you buy one of several different products, each with some limitation. With Final Cut Studio, you get one product that does everything.
I've been using Final Cut Studio 2 for 4 days now and the upgrade is really great. They both do HD and HDV and SD. For working with the HVX, I can tell you this. Both Panasonic (HVX200) and Focus (FS-100) claim the large majority of their clients with these products are on FCP.
With a Mac, you can now run both OS X and Windows at the same time on one computer, best of both worlds.