From a manufacturer standpoint, 4G (for the purposes of this post I mean LTE and WiMax, not 3G+) is a bit of a nightmare. The immaturity of the technology means that chips are expensive and bulky, and realistically offer benefit to only a small portion of consumers. (Compounding the issue, "4G" has become yet another buzzword that consumers don't understand but think they need anyway... but I digress.)
Consider a diminutive device such as the Samsung Galaxy S II. It's thin and light, but could a 4G chip be integrated without expanding the dimensions in one or more directions? I'm no engineer and it's hard to find details that are written in plain English (or my Google-fu is lacking), but I'd have to guess the answer is no. Assuming you had to choose one or the other, which would it be: 4G (but added size), or no 4G (and a sleeker/smaller device). Of course, I could be wrong, but hey - humor me.
You know what to do: vote in the poll and sound off in the comments below. (And since we always get a Melvin or two pointing out that this poll isn't exactly scientific: we know, thanks.)