Yes, really: too much work. Heh, I don't fit into the lazy but desperate group you allude to above.
One of my guys is writing a SL app that looks great. It still took a good amount of (great) work.
Another guy is writing a different part of our suite in HTML (because it's public facing).
Getting it working took more than SL, but not too much because his knowledge is good.
Getting it working on 3 versions of 3+ browsers was too much work, IMO.
HTML & JS aren't the platform. That and 9+ browser implementations are the target platform.
Tweaking the L&F in 2 or 3 libraries' CSS to match and get a consistent look is also too much work.
I actually agree with points in your comment, but as the guys who replied to you point out there _are_ more productive platforms.