There's still plenty of warts, of course, but that seems true of just about every widely used piece of software -- bad decisions early on in development become very hard to walk back later when any of millions of sites/themes/plugins/etc. could turn out to be depending on that bad decision being there...
http://trends.builtwith.com/cms provides some good trends of the big players, but I wouldn't put too much stock in it.
That said, as a developer who has fallen into the WordPress business out of necessity, there are a lot of great products out there that are built much better than WordPress and I wish one of them were the dominant player. Still, WP manages to get the job done most of the time.
Honest question: Can you name one?
I'm seriously looking for a WordPress alternative, but I haven't found one that is truly BETTER.
Sticking with PHP, both http://modx.com/ and http://www.silverstripe.org/ are fairly popular and well-built. I've also heard good things of http://www.concrete5.org/ , http://www.movabletype.com/ , http://textpattern.com/ , and http://ellislab.com/expressionengine . http://habariproject.org/en/ has also been built specifically to address many of the faults in WordPress and other popular systems.
Pity it's so widely used, and there's little competition...