Two comments, one trivial and one more important:

trivial: personally, I don't think any of the jokes are really very funny. Then again, I never really liked the particular formula they're using, and I'm willing to accept that my taste in humour might be a little idiosyncratic.

important: I might be stating the obvious here, but I don't think it's really that enlightening to compare this with human joke-making, as I think they're mostly doing different things. Although the computer can do a passable job at filling in the variables for a given formula, that's a far cry from coming up with the formula in the first place. That's the impressive act of creativity, and after-the-fact mimicry of the same is much less impressive. When a computer gag program is flexible enough to come up with less stereotyped, formulaic gags, then I'll be impressed.

I'm reminded of, for example, EMI, Experiments In Musical Intelligence, David Cope's computer program capable of writing startlingly good pieces in the style of dead composers - but, of course, unable to come up with a distinctive, expressive style of its own.