You mean instead of handing out N invites, just pick N users at random? Why would that be better? You confuse and potentially upset the randomly-chosen users, and you disappoint the eager people who actually want to try the new thing.
Fact is, they can't satisfy everyone. The algorithm used to differentiate the few from the many will obviously upset some groups.
Would you rather they charge for it? That'd be the Microsoft thing to do [1].
[1] http://www.theinquirer.net/inquirer/news/1011983/microsoft-t...
Also, for Google I/O it would have served to have people apply, and review applications to pick real developers and not dumbass unable to read a line of code but hoping for a cool gadget to flip on ebay.
Anyway, as much as I want to try the new map right away I would do the invite system like them: you get to ramp up your userbase progressively, and people trying it actually want to try it (not grandma opening Maps and being completely confused by the new UI and possible bugs).
Gmail and Google Groups have both had random rollouts for changes, with optional rollbacks. That seems more fitting (to me at least).