I honestly doubt any of us will live long enough to see the day when IE comments won't need to be added to CSS, JS, and some HTML to make things look right.
1) Highly likely.
2) Highly unlikely.
* SIGH * so all we get are a couple of new tags...Video and canvas and we're back to square one, with trying to get it to display properly on the different OS / Browsers available...
Will HTML 5 pages display differently on different OS/browsers???
Surprisingly enough, the actual tag elements display reasonably consistent across the browsers that support html5. The real problems start when one try's to use the html5 api's or other elements such as html5 forms or video.
As a developer will HTML 5 negate the need to develop for each OS/browser?
Only if you wait at least another 5-10 years before implementing. HTML5 is not supported in any version of IE, (except IE9, which is only in the preview stage of development) and given the fact that IE6 is still in use, (10 years after release) most of the features of html 5 and all of css3 will not be cross browser compliant until IE8 usage can safely be ignored.
the joys of HTML...
I don't get why it's so difficult why all the browsers can't display X the same...
It should be like math, 5 means 5.
But rather it's like colors, "blue" do you mean dark blue, or light blue, or ocean blue etc...etc...
There's an excellent article discussing HTML5 on A List Apart.
To quote a few points:
HTML5 is "evolutionary rather than revolutionary."
If you are currently creating websites with any version of HTML, you’re already using HTML5.
If we had waited for every browser to completely support CSS 2.1 before we started using any of it, we would still be waiting.