In a general context, a company practicing 'predatory pricing' may do so to drive the other competitors out of business. Once that happens, it's free to raise prices to monopolistic levels which would end up hurting consumers eventually.
These fears are not based on evidence. When has someone released a free product only until they wiped out all the competition, proceeding to jack up prices? I mean, once they jack up the prices there is an established market ripe to pick customers from. Furthermore, the temporary profits, if any, would only be temporary and would be a greater cost to their corporate image.
So my question to the Google nay-sayers is do you expect Google to raise prices on Android once they have forced MS and Apple out of the smartphone market? Or do they just have a superior product model in which they can offer free software and make money on ads while their competition must charge for the software. I personally don't think they will ever raise Android prices so it's just good competition.
More likely their intention is to keep it free, but with additional "conditions" such as Google search being the only way to find information. Mandated use of Gmail, Google Docs, Calendar, Contacts. Heavily integrated Google Plus social features like chat, blog, and photo sharing.
Google won't need to charge for Android because there will not be a way to avoid a Google tentacles if you use their OS. Google is trying to burn down the ecosystems of it's competitors with free products and make money by being the gatekeeper of your every activity with a smartphone.