I think that Europe vs America (actually, USA) is a difficult competition to analyze.
The USA is ONE country (albeit with many different states) whereas Europe has many countries, each of them with their own fashion. And then fashion changes too depending on each region within a given country.
You cannot compare Italian, British, Spanish, German or French fashion, to mention a few. I can spot a French, British, Italian or German person just by the way they dress, especially on women.
By extremely general terms, French are classier, wearing longer skirts, shorter heels and blouses, Italians are more fashion forward, glamorous, sexy and posh looking (think Vicky Beckham), British are loud, skimpy and colorful and German women look usually more sensible, comfortable and relaxed (but still young and fun). I always thought Spanish fashion was ok but after visiting the UK I think we are rather neutral and boring. I wouldn't say Spanish women dress comfortably, not really, but it does happen in Barcelona, a city where people commute mainly on public transport. I've heard it's rare for a young woman in Sevilla to wear flat shoes though, and from more than one person.
As for the American women, it strikes me how you combine colors. You don't see women dressed like Shannon, MaryK or Rae, to name a few, on the streets of Barcelona, which btw is the most modern city in my country, and the most cosmopolitan. We do not mix bright colors or loud prints, period. I'm not saying it's wrong, or bad-looking, just highly unusual. People would stare. A lot. Unless you were an actual tourist, in which case we would assume you are a 'guiri' and therefore just dress weird.