So the Duke Law Journal actually wrote a research paper on acquihiring:
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2040924
The summary:
Acqui-hiring makes no financial sense to the buyer and it might not even make sense to the entrepreneurs to “leave money” on the table by compensating investors since they could easily bail.
Basically acqui-hiring is the result of Goodwill and too much money. Big tech companies have tons of money, entrepreneurs who join big companies are getting fat signing bonuses, so why not let the investors have a piece of it too.
After the bubble bursts, this period of hubris will be noted by this ridiculous concept of an “acquihire”