You're going to have to broaden your perspective in order to see all the diversity. Going by your logic of assigning robot types simple labels, I'd say that 2007's game was even less diverse than this year's game. There were three main types of robots in '07: Ramp-bots, Ring-bots, and Ramp+Ring bots. But... if you wanted to look into those three categories, you'd see amazing feats of engineering and diversity. There were pneumatic ramps, two-jointed arms, four-bar linkages, etc.
Take a look at this year's robots. On the outside, they may all seem extremely similar, which I personally think is due to the bumpers this year (yet some teams like 1501prove me wrong
). They all may look like red and blue squares and rectangles on the outside, but you have to look a little deeper. Most 'bots have a possessing mechanism of some kind, whether it be a pincher-roller set-up, a single roller, or a vacuum. (Hey, that's three types right there!)
Look at the hanging mechanisms this year... There are some teams that drive up the vertical bar, there are some that grip and flip themselves over the vertical bar, there are some that grab the top of the tower, etc. Not only that, but the means that these robots accomplish these feats: scissor lifts, winches, pneumatics, gas shocks...
Look at all the drive trains this year... There are, of course, your standard four wheel drive, six wheel drive, and swerve drive (dare I call a swerve drive "standard"?
It is becoming increasingly common, however.) But, have you ever seen so many Mecanum drives attempted by so many bots? How about eight wheel drives? What about
articulating eight wheel drives? And then there's that non-a-drive.
Now... don't you even get me started on 469. Heh.
TL;DR: Are the robots similar this year (And most years, for that matter)? In a very broad sense... yes. But if you look a little closer... no.