Hmmm... I would have to say I have that the government is its own unique thing. It's kind of a diarchy, not a common type of government. And while lesser nobles seem to be put in place, (I can only assume by bloodline, as I can't honestly see anypony voting for Prince Blueblood,) in a fashin similar to the British monarchy, the "high princesses", those who are put in positions of highest power, are alicorns, a state which, by all show canon to date, is something that is earned through virtue and a deep understanding of the power of love and friendship. (To stem the inevitable alicorn debates, Lauren Faust claimed this herself, as well as the other show writers. I could debate the matter further, but that's not what this post is about, so please don't debate it here.)
Regardless, the title of "high princess", (one who is an alicorn,) is one that is earned. Whatever forces determine the ascension of a princess are the guiding force, adding a touch of theocracy to the mix. So as for government, I would say that Equestria seems to have its own thing going, although it does lean more strongly on European monarchies.
Culture is, from what we have seen so far, widely dominated by a mix of European for the unicorns, (largely English, but with a great deal of French, along with some Russian, German, and smatterings of numerous other European countries,) American for the earth ponies, and Greco-Roman for the pegasi. I can't really say which culture is the more dominant, but they appear to have an equal balance so far.
Geographically, it.... er, actually, I stink at geography. But taking a look at the climate, it seems rather European. Or maybe Middle Earth.
And most of the indigenous mythical creatures seem to be of Greco-Roman origin, so I suppose that must be taken into account.
My final conclusion is that Equestria is... well, it's kind of it's own thing. Not entirely English, not entirely American, not entirely Greco-Roman, but a balanced mixture of the three.