Yeah, I don't think the "I like DVDs" comments are really valid as they are inevitably going to just stop being circulated within years as Joshi said. Blu-Ray and HD-DVD offer pretty much the same leap forward that VHS to CDs offered, and CDs to DVDs; with them holding over 30GB each, that's a lot of data capacity.
As for standard definition and high definition, if you can't see the difference then you absolutely must be using a non-HD television or perhaps just a small television. Imagine opening a video file on your computer that fills about a quarter of the screen, then imagine opening one that's the size of the whole screen; clearly, the larger one is going to look infinitely better in full-screen on larger monitors than the smaller one. However, if you were to play them both on a small monitor you'd likely notice little difference.
There's also the fact that LCD and Plasma televisions have much sharper images than unavoidably blurry CRTs, which means that suddenly any flaws in the standard-definition quality are suddenly really obvious. For a quick example, try opening a small video file on your computer and then making it full-screen; that's pretty much what happens to a standard-definition video when displayed on a HD screen, due to its much higher resolution than a traditional TV.
Despite all the marketing bullpoo, all HD content is is a less-shrunken video file -- the quality improvement speaks for itself. What confuses people is needing different TVs and stuff, and them only supporting certain resolutions ("780i, 780p, 1080i, 1080p?!"), etc.