Re: Not really an occasion for "this is America, after all"
In England and Wales at least, an advertisement is an invitation to treat; if a customer likes the offered terms then he makes the seller an offer; if the seller accepts the offer then that's a contract. E.g. that's why the well-known wisdom is that if you see something advertised at what's obviously the wrong price then you can bind the seller to that price only if they confirm the order — that's the point at which they accept the contract you offered.
The main relevant constraints are those terms that are implied and which may not be overridden (that's the Sale of Goods Act-type stuff about products being fit for purpose for a certain period, etc). There are also caveats about "mere puff" — statements that are clearly subjective and not intended to be enforceable, like one cafe's being the best cup of coffee in London or a particular make of car making you more popular at work.
With the Pixel it sounds like the terms suggested in the advertisement were specific and intended to be enforceable, and the contracts formed between Verizon and the consumers were exactly on those terms.
Even though a lot of the specifics are post-1776, US and British law is similar enough that it's the only area I can think of where a US case is commonly cited in British courts as being sufficiently informative as almost to be treatable as a precedent — Shuey v US on the extent to which the revocation of a unilateral contract needs to be communicated (though, oddly, I think British people tend to take it to be that the revocation must have the same notoriety but US people tend to think it must go through the same channels, so the conclusions drawn are not quite the same).