Personal philosophy: some day, all TVs will be HD, including the cheap ones. And then if you want your videos to take advantage of your hardware, you'd have to go back and buy them again.
I've always acquired media in the highest quality format I could. I ripped all my CDs to 240kb/sec VBR MP3s in the late 90's, even though it meant buying a larger hard drive back then, just so that I wouldn't have to rip them all in the future if I wanted them higher quality later on.
As soon as the HD format war started, I stopped buying DVDs until BD won and I could afford a BD player, because I wanted the longest time possible before my media was obsolete.
(Though admittedly, I don't even buy very many discs. I find I don't frequently watch them more than once or twice anyway.)