The lack of empirical evidence is due to that non-compliance. The same browser sometimes allows non-compliant code and chokes on valid code. This is a coordination game (just like driving on the right side of the road). If everyone complies (developers, browsers, etc.) things work. If enough don't, everything breaks.
Have you ever tried printing a thread? It's bearable, not certainly but pretty.
The point being that there is a lot more to development than keystrokes.
But let's user your argument anyway: what's faster:
<div id="content">content</div>
or
<table id="content"><tr><td>content</td></tr></table>
Now, lets say I want to move the table text from left to right alignment. While you're mucking around in your code, I pull up the css file and add a line.