what do i really need 1080p for?

if my only intention of getting a plasma/or lcd is to buy a new tv, that can accept the high def signal in the future, what do i need a 1080p tv for? arent they only really useful if using a blue-ray type source? my intention is to NOT use this as part of home theater , or even to watch dvds..simply watch cable tv. that being said...looking for 46" isnt plasma the way to go? ive got a sony 36" Wega XBR and not much rivals that...so whatever i get needs to outperform it. And 720p of course is way less coin.