Well, I think we all know he's lying about the hardware being better than high end PCs. I'd be willing to put money down that my 3 year old desktop is at least as fast with an i5 750 quad core at 4.2ghz and a pair of 5850s.
That said, I think he does have a point in the software department. Why? Well, because they're developing software specifically for a home entertainment environment. I use a media PC hooked up to my receiver to watch movies and TV shows, and it can play games although I don't bother since I have my desktop... Anyway, the point is that I still have to navigate Windows on a TV from across the room using a wireless mouse. It works but it's a bit of a hassle. There's some software that helps with it a bit, Windows Media Center is okay, as is XBMC. Then you can alt-tab to Steam with Big Picture, and of course zoom in on webpages/YouTube for that stuff... But it's definitely not as nicely integrated. So, they do have a slight advantage for the home theater PC market.