Animal~
When I say "The impersonal world of the Internet", I mean that we are sitting looking at computer screens rather than at "real" people. Most norms of our day-to-day culture don't apply over the Internet--but since we're human, we still try to apply them.
On the Internet, we can't see a person's face or hear his voice. We don't even (usually) know the person's real name. The only contact we have with others is through written word--and this is where the problems start.
Humans are used to communicating through a combination of body language, words, tone of voice, and situation (you talk to your boss differently than you do to your best friend). Online we have only words. Despite this, most of us still try to use the same words we would use in a "normal" setting. Without things like body language or voice tone to support what we say, the meanning of our words sometimes becomes lost.
Compounding the problem is the fact that many of us are from different countries. Each country has its own customs, and its own way of speaking. But when we read something, we always apply the norms of our culture to what we're reading. This too can lead to misconception, as an offensive statement to one culture might be (and often is) perfectrly acceptable to another.
Eurpoeans are naturally somewhat better at bridging the culture gap than Americans are, because they often have to do it on a day-to-day basis. Keep in mind that most Americans have never been out of their country, and have never talked to someone of a different culture. Consideration for other cultures is NOT something most of us have ever had to deal with before--myself included.
Likewise, Europeans are so used to dealing with other cultures that they tend to forget that Americans AREN'T.
To apply all these ideas to the original statement--
A person from the USA calls himself an "American". He simply calls himself that because that's what he always has, and there really is no better word to use.
To a European, this lack of consideration for the people from other American countries can seem like arrogance, almost as if the USA resident feels that residents of other countries don't count as humans.
From there, the minsuderstanding starts, and rapidly increases until we have....well...this thread on the messageboard.
The best thing for ALL of us to do, is assume that ALL comments are in good faith and not intended to be derogatory, unless it's BLATANTLY OBVIOUS the intent is otherwise (eg. "You're a f***ing S***head!!!")
J_A_B