After all, there's always another website looking to take the users that you're not willing to fully support.
For a while, some die-hards will probably try to use Flash to mimic the experience that HTML5 and these new CSS features offer. But I think the uptake of Flash amongst new developers is less than that of standards-based practices. Simply by virtue of having more developers supporting the standards based approach, I think Flash will eventually be eclipsed until it is relegated to a niche, kind of like how Google Maps is everywhere now and MapQuest is dying.
There is this big assumption that users are resistant to change. I'm inclined to believe they're resistant to unnecessary change. We just need to make them feel compelled to change and users will do so. For the first time in a while, Safari and FireFox actually have compelling features to users that IE does not. That changes the landscape quite a bit.
From a business point of view, especially in the marketing world, you'll have a hard time compelling the every day firm to ditch IE support. And as I said in the previous thread about this same exact thing, the elites can do it and still get plenty of business, but is everyone in the position to be able to turn down a job because of this?
The answer is probably no.
EDIT:
I guess the real issue is more along the lines of an education issue, and people who don't grasp it, getting put in charge of whatever new micro-marketing site you're releasing this quarter.
While many users may like these things, "demand" seems a bit strong.
And then there are the folks who don't like "cool desktop-line animations/transitions".
most users seem unable to determine what a browser is. I think you have wildly unrealistic expectations of what real users want.