Well, I wouldn't say I "prefer" SD DVD over HD, but there are several reasons I'm satisified with it:
1) Much better selection of movies. Right now, HDM is too new to offer the kinds of choices I like in my viewing. There are some movies that barely made it to DVD, much less eventually make it to HDM.
2) Price: DVD is dirt cheap. No, scratch that....have you seen the prices of topsoil? DVD is cheaper.
3) Many DVDs have beautiful transfers that look great on my TV. Meanwhile, there are a decent number of "bad' HD transfers out there. For example, "The Cowboys" on HD DVD is a pretty poor transfer. The DVD looks nearly as good. In addition, some DVD transfers (like Cars) look so good, it's hard to imagine the Blu-Ray version looking that much better on my somewhat small (40") screen.
4) The format war is all but over, but until one format officially gets the boot, I'm gunshy about buying in fully.
5) Blu-Ray (which looks like it will be the winner), is still a wee bit out of my price comfort zone another $50 - $100 cheaper and I'll probably be in.