I just (re)built my HTPC and installed an i5k with the HD4000, and it has played all of my media without issue so far. No dedicated video card installed/wanted/needed here. Saves money by not buying the Graphics card, and not having to power the card, and no more nVidia driver issues!
I wouldn't wait for the i3 with HD4000, since I'm not even sure how long before you could get one.
As for Win8, I have NO plans to upgrade to that ever. That could change, but I suspect it will be a bit like Vista, never quite right, and the next version will be a lot more solid, which is when I'm planning to upgrade, if ever. Windows 7 works great for my current HTPC needs.
I also agree that you should consider building your own computer, but certainly understand that it's intimidating for many people, and if you do manage to break something (hard to do), it kills any money you would have saved.