I think a lot of Americans are very frustrated with what they see as not only a government that doesn't represent them, but also an electoral system that leaves the majority of people in the middle and the moderate left completely unrepresented. I don't think any of the people who say " Why isn't this happening in America" really want the bonfires, and the riot police, and the rubber bullets. What they want is an end to what they see as a highly corrupt system in which they have no representation.
I also think that the people who say that sort of thing are also incredibly upset (and frankly, rightly so) with the ability of those in power to use mainstream media to control the message; or more pertinently, diffuse the message (as seen in media coverage of OccupyWallStreet, not to say that OWS was necessarily a movement that deserved to succeed) or remove the message altogether by not reporting it at all.
Do I think the American people are in a place where their problems can be compared to those of the people of Ukraine? Well, I don't think is suffering is like a penis game, where you whip it out and measure who's got bigger problems. That being said I think that Americans still have the ability to improve their lot by getting involved in the democratic process, whereas the people in Ukraine do not.