I think if you look at the specifics of Intel's claim, it's not that HD4000 will replace your $400 graphics card - pretty hard to do that given the silicon real estate and power envelope constraints.
What they do say is that for most people (and OEMs building systems) they can save the expense of an add-in card by just using HD4000. It saves money, saves power, and for 99% of the things a computer is used for, works as well or better than the typical add in cards/chips used in systems.
I'm not a gamer by any means, but I have not found anything that I have thrown at my HD3000 (last year's model) that slows it down or shows any need for anything faster.
HD4000 is a pretty good graphics solution - especially for video, and even for basic gaming. The audience in this forum may be excepted from that of course, as this is not a normal cross section of the target user base
My comments are my own, not those of my Employer - Intel. I do not speak on their behalf nor do any of the statements above reflect any official comments or positions or marketing jargon from them.--
"We are half-hearted creatures, fooling about with drink and sex and ambition when infinite joy is offered us.... We are far too easily pleased." C.S. Lewis