That seems to be a tendency in the US. While in many European countries moderate right and moderate left become centrist over time (making it hard for the electorate to discern what is what, which can become an issue too), Democrats and Republicans seem to grow apart more and more, finding little they can agree on, even on such fundamental and long-reaching things such as a healthcare reform. It's not a good thing if half of the population always feels subjugated if it is ruled by the party elected by the other half. I didn't vote for Frau Merkel and probably never will, but I don't believe that she is set on destroying Germany for me.
I don't know why this US party radicalisation is - it defies expectation that as a state system matures everyone moves towards the middle - and why it is so pronounced in America. You've been a democracy for more than 200 years and contrary to some prophecies no Democrat or Republican administation has yet brought about the downfall of your great country. All Americans I meet seem to be neither Michael Moore nor Rush Limbaugh, but somewhere in the middle between the two, which appears to be a sensible political position for an adult with an acceptable IQ and not under the influence of drugs. Yet it seems to be the fringe constituencies that are pampered.
In Germany, parties certainly do lip service for their fringe constituencies, but they know that elections are won in that huge amorphous grey in the middle, populated by that evasive creature called the swing voter. And it is largely for him that policies and laws are made.