the same intel cpu's are available for both mac and pc, yes? but, when you buy your macbook-pro today, in 6 moths time when a new cpu comes out, can you upgrade without buying a new mac? the answer is a big fat NO.
ok, so lets talk GPU's can you upgrade a mac's GPU... oohp, heres another big fat NO for ya.
can you upgrade its ram.... oh dear... another fat NO.
so how can anyone say a mac can compete with a PC when a PC user can simply upgrade whenever the f' they feel like it? "oh my new video editing software doesnt seem to like my sli-nvidia 7900gt's, i will just go grab a new x285 for a laugh and see how it does"
and yes i am aware that the big boss of mac's (whatever the f' its called) is an awesome machine, but give me the money you spent on it and i will give you a 8 core CPU xeon, (potetially) 16 core GPU, server class ram, raid 0 box which would THUMP any mac for anything you chose to do.