What this Reminds Me of
The well known tactics for getting someone hooked on drugs, first few fixes are free and when the guy gets dependent on the stuff, it's pay time.
Google does have the legal right to do this, after all, all of their license agreements give them the right to do whatever they want. The thing is that they have been less than open about how things are going to work out.
Until fairly recently, there was a sense of Google's being a technologically brilliant "Do no evil" company that develops all that cool tech for their own needs and then also shares that technology with the rest of us (unlike the other corporations which like to jealously sit on the stuff their R&D departments make); at that, all of those products and services were in a "perpetual beta", which was often perceived more as a philosophical stance than a technical one, as they were often capable of rivaling other companies' fully developed products, and all of them were free.
That was obviously a myth, but rather than be fair and honest and openly say "This stuff is free for now, but once it comes out of beta, it will cost you, possibly in the ballpark of $x per month/developer/whatever.", Google decided to let that myth live as long as possible, and it doesn't take a huge leap of faith to conclude that that was because they benefited from it. So they purposefully waited until the last moment and then just said: "You've got two weeks to start paying or GTFO."
And the users suddenly found themselves locked into a service they have to pay for and which can arbitrarily change its terms and conditions and pricing. Google, on the other hand, first had an army of people who first conducted testing for them for free; Google then allowed them to keep using the polished up service free of charge for a while, right until the moment Google estimated the bulk of them was committed enough that they'd have hard time getting out, and that's when they said "Pay up!" One may say that the users turned out fairly naive, while Google turned out rather... cunning.
So, while Google may be legally covered, this is a warning shot to anyone using any of their "free" products and services. Though, speaking of legality, it remains a fact that Google has used its cache and the guise of "a beta" to offer a commercial grade service for free for some time in order to get people to chose their service over a competing one and that might well be anti competitive behaviour.