Sorry, would you care to elaborate? I'm not really sure what you mean by "the M&A department the first time around". I think the fact that only _some_ of the team members are ex-Googlers is significant.
Additionally, what other business case could their be to purchase such a small, new company. Couldn't Google just have integrated these features into their shiny new Buzz service _last week_ and have overshadowed Vark very quickly?
If you quit a company, do a successful startup, and then get re-acquired by the company you quit in the first place, chances are that you don't want to go back to work for them again. If you did, why did you quit your job in the first place?
Though in their case, with 4 founders, $6M invested and a $50M exit, it's not "that much" money.
I wouldn't spit on it obviously, but considering some of these guys' former positions at Google, they had probably made a good amount from stocks and such. What I'm trying to say is that it's probably in the same order of magnitude of their worth before that.
It would depend on the events which led up to leaving Google in the first place. I doubt the original team left Google because it wasn't challenging enough or there wasn't enough flexibility, both of which would be reason enough to leave a lesser company to go out on your own. If your logic was accurate, then why would Aardvark have even sold out to Google in the first place?
Possibly these people liked their idea enough and though they could make a lot more going it alone, now they like the idea of Google support in perusing continuing to peruse their idea.
Just a guess really, but what they are doing now make be considerably more exciting than what they were doing at Google previously.