This thread reminded me I wanted to write my own browser.
Several years ago I looked at HTML 4.01 and it wasn't exactly trivial, but today I glanced at HTML5 and... HOLY FUCKING SHIT WHAT THE BLOAT DID THEY DO?!
The same with CSS3 vs CSS2.1, it seems they just want to pack as much useless trivial flashy distracting shit in there as they can.