Please use http://meiert.com/en/indices/html-elements/ instead, as it’s based on the WHATWG HTML Living Standard rather than W3C’s versioned fork.
1. What are the differences? I've no idea what the significance of the source is.
2. The one you linked is hella unreadable. OP's table is, due to the color differences, extremely easy to skim, while the one you linked has only very similar black&white x and checkmark symbols, which require closer inspection to differentiate.
The WHATWG doesn't bother with versions, there will be no HTML6, for example. They just continually update the HTML5 spec. It's a living spec.
The W3C kind of tracks the WHATWG progress and tags certain points with version numbers (that's where the "5.1" comes from).
Although they do some development on their own, and sometimes both sides disagree and the specs diverge. At some point WHATWG removed an element that W3C retained or the other way around.
I have no idea if they still diverge. I just discard the W3C when it comes to HTML5 and follow WHATWG.
Well, practically speaking, I follow what the Mozilla Development Network documents. :-)
Yeah, I don't quite know when such a table is very useful anyway. What I check is: (A) http://www.whatwg.org/specs/web-apps/current-work/multipage/... (B) http://caniuse.com/
With the notable exception of Microsoft.