but with HTML, you get to see the problem that faces open standards. people don't *have* to follow the standards when they write their programs (eg, internet explorer ). as a result, if you want to deliver an electronic document halfway around the world, you can't garuntee it'll look exactly the way you want it to. this goes far beyond simple formatting issues, btw, because there are large discrepancies in the ways that different browsers render HTML.

with a more tightly controlled format, like a word document or a PDF, you can more or less control these issues.

besides that, HTML offers no compression, or any way to embed images or fonts, and often requires multiple files. it's not ideal for a "portable" format, which would ideally contain everything it needs within single file.