I went and read through the most recent comics. I think his inability to draw faces is surpassed only by his inability to draw hands. Also, what's with the release schedule? It appears this is the artist/author's full-time job and yet the strips are released very inconsistently. Some of these web comic strips are posted weeks or months apart. Why would a comic with so little effort put into the art, in both the long and short term, have so many fans? I guess he's living the dream, and his fans are living vicariously through him.
He clearly puts a lot of effort into the art, and I think it's pretty good overall. Apparently a lot of people here disagree, for whatever reason, but I've always thought MT looked good... okay, maybe not the hands, but overall. And it's improved a lot since the early parts of the series, as is very clear when you look at it. But yeah, it's reasonably good now.
You are right that he's lucky to have such a lasting fanbase, though. I mean, I do think that the story is more interesting than almost all webcomics, so that is deserved (I am one of those people who's kept following it for a very long time now, after all!), but he has definitely been lucky. Lots of webcomics have never achieved anywhere near MT's level of success despite also being good and updating much more regularly, though MT always has been one of my favorites.
As for why there are so many delays, there are a lot of reasons, some good, others not. Whenever he makes a book, that puts in a long delay as he works on redoing stuff for the book. Health issues (his recently, his wifes' before that) have delayed things. Surely having a child didn't help. He's slow at drawing too, I believe, so pages take quite a while to do -- and he's a perfectionist, so he often ditches completed panels of pages when he doesn't like them, puts huge amounts of detail into backgrounds that you can barely see at the resolution that the comics are posted at (he draws it much larger), etc. It doesn't help that he's often working on the script of each page until the last second too.
Also, it seems that he frequently prioritizes working on stuff for the store over making new pages. You know, fulfilling orders, having new stuff to sell there, etc. That's important of course because that's where the money (for him) is coming from.
EDIT: I also got a chuckle out of the "characters" page on the website which has only this posted:
"All right, all right! I still don't feel like finishing these sections, but whatever (grumble)...
piro - fall 2007
Believe it or not, the (page) is in production and will be incorporated into the new site launch. We just are not including them as part of this beta test (because they still need some work)."
Please take my money sir!
I have to guess that he's left those pages there as much as a joke as anything... I mean, everyone knows that they'll never happen.

Anyway, if you want those details, there's a pretty solid MT wiki out there.
As for this though, I am worried about the game being finished of course, but with money like this behind it, I think that'll push him to prioritize it.
I wouldn't be surprised if it leads to few comics being posted for a while while he's working on this, though, of course. Ah well.