Do you mean will current computers be obsolete when HTML5 comes in? Absolutely not. A lot of stuff in HTML5 is all about getting more out of the web while using less resources. HTML5 will require less computing resources than comparable Flash does now.
Currently in tech, due to the new frontier being mobile (which includes tablets), the push is to do more with less. The race for higher and faster CPUs has basically plateaud. While desktops and laptops are getting more CPU cores, instead of faster ones, new operating systems are being written from the ground up (iOS, WebOS, Android, Windows Phone) to handle less resources.