The digital changeover is to give more bandwith 'in case' the TV stations need (or want) to broadcast in HD. My local stations are only broadcasting (over Timewarner) in digital standard def until primetime, then select shows are in HD. Even then, their idea of HD is 1080i (if you're lucky, most of the time it's 720i max), not 1080p, so it it looks much better than 480i, but it's still pretty crappy (at least on a 60" Sony SXRD and a 42" Philips LCD). Interlaced signals just don't cut it.
The converter box will down-sample the signal to whatever your TV can handle.
And to answer the subject of this thread...
YES! HD is a scam! The millions and millions of TV shows and movies that were shot in SD (or less) are never going to be remastered into HD, so only the ones that are now being shot in HD are going to look worth a shit. I can only hope that after the changeover they will start broadcasting the new stuff in progressive scan instead of interlaced. (720p would be fine, 1080p would be better!) Otherwise, Blu Ray is the only thing that takes advantage of the 1080p capabilities of my very expensive televisions. (I'm not bragging, I'm just pissed that I spent a boatload of money on these HDTV's, and the only thing that makes it look good is a BD, and a select few PS3 games.)