Localization is clearly one of the prime disambiguators for Google. If you switch Instant off, you'll see twice as many suggestions, and thus more geo suggestions become apparent.
But almost every new Google search feature I've been seeing seems to be built for disambiguation, including (but not limited to) the returning of general terms in localized serps. Instant and Instant previews, eg, are in a way an extension of Suggest... and a different angle on the choices.
You can also see variations in Suggest that aren't geographic, but which are cyclic. Eg, I regularly search some financial data and notice that Google Suggestions periodically include 'google finance' as additional terms in the third or fourth spot.
I can go a month or so without seeing Google Finance suggested, and then suddenly it will be suggested for a month or two before it disappears again. This is independent, as far as I can tell, of cookies, browser, logged in or out, location, or of what I click. I almost always keep search history switched off. This pattern has been repeating consistently over a long stretch of time now, for well over a year.
I should perhaps graph it or keep better notes, but I haven't, in part because I don't have click-through data to compare, and in part because I can't assume I'm seeing what everybody else sees. The observed dates of change don't appear to correlate with serp and traffic changes I see reported in the forum.