Daddy, I think it's funny that you claim that you don't understand the grouping, right before you explain it; both cases are driven by demographic reality, a large number of educated young people dissatisfied by both their job prospects and their political environment.
Certainly Libya was all about American planes; but for Egypt and Tunisia, I think "pressure by US and European military forces" is wildly inaccurate. Tunisia happened so fast, the West hardly reacted at all, did it? It's possible Mubarak might still be in power if the US had backed him as aggressively as we backed the government in Bahrain, but I'm not sure. I'm not sure any US approval for violent repression would have restored Egypt's economy (which is based on tourism, transport, and industry -- not oil -- and therefore highly vulnerable to unrest) fast enough for the generals. The US government basically did nothing beyond making some equivocal noises about human rights; that is something of a shift (towards rationality) from previous policy, but I think it greatly overestimates US competence and influence to suggest that the Egyptian revolution "would have gone nowhere" without it. Of course it could probably have been crushed; but it could also have been crushed in the face of our equivocal noises about human rights. Syria is having a lot of trouble crushing its uprising, but American and European grumbling about civil rights has little to do with it. Maybe the generals would have gone to more trouble to keep Mubarak around if they thought he was a huge asset in terms of currying favor with the US... as things were they thought he was mainly a liability, but not mainly because of the US.
I don't think OWS will have large short-term political effect, largely because of its decision not to go the Tea Party route and cash in its chips (in the form of press coverage, motivated activists, popular opinion, and so on --the big difference in deployable political assets being that the TP had more backers with money --) by being co-opted into an organizational arm of, or caucus within, a political party. I think this is probably a good move in terms of OWS's goals. Whether it has a longer term effect remains to be seen. Were the Summer of Love hippies, or the French 68ers, "of consequence"? In terms of short-term political goals, not particularly, is my impression (or maybe only in getting Nixon another term via a mess in Chicago)? Medium-term, maybe the hippies had some effect on us getting out of Vietnam, though that's probably overstated? You would know better than I. Longer-term, I would say they had a large cultural effect -- everything from the New Left capturing academia, to a change in social and sexual customs (as part of a complex interaction with feminism), to a certain effect on political culture (largely everyone from now on having to make the case that the war they want to start is WWII and not Vietnam -- though that may be giving them too much credit?) to therapy modalities, to the plots of movies.
That the OWSers are going home when it got cold does not mean much (their forerunner, the occupation of the Wisconsin state house, happened a good deal earlier in the season). And I certainly wouldn't underestimate "easy sex with strangers" as a political force. Actually, if OWS can habituate large numbers of young people to the idea that political protest is not a dreary duty of enduring strident political speakers and remaining on message, but a Bacchanalian revel full of excitement of all kinds, turning it into a regular and frequent ritual, that could really change the political culture.
My impression is that in the early days of the AIDS crisis, ACT UP, for instance, was good at conjuring that atmosphere; the Seattle anti-globalization people had a bit of it but not quite the same vibe. Both of those only reached a small niche though. Whereas the blogosphere is full of people describing their surprisingly inspiring trip to an Occupation.
Of course, maybe that's just because there's a blogosphere now; but, then again, there's a blogosphere now, which also changes the playing field. OWS's "leaderlessness" makes it easy to dismiss, but I think this is one of the interesting things about it -- cheaper, faster communications have always driven social change and transformed organizational functioning (printing press => Reformation, etc.) And the "leaderlessness" and self-organization via social media and cell phones and the web is, of course, another similarity of Tahrir Square and OWS.