Brian, welcome to the forum.

Well, where to begin?
Are all those people who have been engaged in a past HD DVD vs. Blu-ray fight (or wisely haven't), who have bought (often replacing their previous DVD) and discussed many HD discs now, the ones who have produced them, often after a painful restoration of worn-out elements, and so many people more who are involved in the HD experience and the manufacturing of equipment and software, are all those people simply nuts and idiots?
Let's even skip the discussion of the new (higher sampling bandwidth and/or lossless!) audio formats (codecs) on BD for a moment, they're simply not present on an SDVD, and let's concentrate on the image.
First of all: yes you need new HD TV sets (or monitors) alright. Yet, I can assure you that even on a classic TV set the difference is already obvious very often. Why?
Because the colours are deeper (better defined) on a Blu-ray, and because many old TV sets have a better resolution horizontally (ability to display pixels across the horizontal line) than the necessary minimum for NTSC. So, even on an old TV the image is often visibly better already.
But never enough, of course.
You can start with a 480x720 pixels on DVD image and upgrade it nicely to 1920x1080, and the result may indeed be stunning already if this is done well, but do you (I know I should say: "they") really believe that resolution can be
added to a picture? That information that isn't there can be guessed by the circuitry? That the image suddenly contains more spatial information than was recorded? The answer is, of course, simply: no.
It is true that the newest generation of HD TV sets do a wonderful job when pumping picture resolution up to their (the TV's) native resolution. It's also true that perhaps you won't be asking for more if you never saw a real (and good) BD presentation in the first place, or if you're only looking at a 37" (or lower) screen or whatever size you happen to have , but unfortunately from too-much a distance.
Or if all you (they) ever saw were HD broadcast channels (720p at best, and often compressed to an inacceptable level during transfer), yes, that may make you think "no big deal".
Hint 1: it takes a well-done BD (and many are
very good!) to judge BD.
Hint 2: one can, and one needs to, sit closer to an HD TV than to a classic NTSC screen. The individual pixels need to reach the individual rods and cones.

But even when watching it from a slightly bigger distance, the difference between a very good DVD when upgraded on one hand and a very good BD on the other is simply stunning. Yes, the upgraded DVD is VERY acceptable, but the BD sort of make your eyes pop out. It's not just the resolution alone, it's also the colours, and the better compression (much less compression, because of much more available space on the disc, and new better codecs).
A simple case: upconversion cannot invent skin texture (or any surface texture) that wasn't recorded on the disc. You definitely will see the difference!
And then, yes, the audio....

Cees