If you go by history of the PC's just sit back & watch these tablets and phones evolve, they will get better processing power as they develop, only matter of time.....For the "couch surfers" yes it can replace a pc. But for gamers/photo & video editors/CAD users/etc there is not enough processing power to do what they need on a tablet.
CNET has an article about this here: Six scenarios where the iPad is trouncing the PC | Apple - CNET News
Do not delude your self, technology is improving all the time "FACT" not fiction.....