Well, HTML is nothing like XHTML, that's for sure.
Saying that HTML 4.01 is not really different from HTML5, that may be true.
The reverse though, is far from true. HTML5 in not an addition to HTML 4.01, but HTML 4.01 was made an addition to HTML5.
Learning HTML 4.01 is a smart thing to do. But starting off HTML5 after learning HTML 4.01 will make for a lot of "unlearning". Learning XHTML 1.0 won't make it any better.
Of course, that would be true for those passionate enough to call them self web devs. For the rest of coders wannaby, any HTML would do. Is not that they can tell the differences anyway.
And this is a topic that should shout loud and clear: IT MATTERS WHETHER YOU LEARN HTML 4.01 OR XHTML 1.0 OR HTML5. 'Cos it does. The web is full off coding simulators as it is. No need for SPF to help thickened them lines.