I disagree with the claim they are. Democracy is about choice by the voters. 2 choices is not enough choice. Furthermore in the contemporary USA, 98% of the time incumbents are re-elected if try. So really it is a 1-choice system. Congressmen are more likely to die in office than to lose an election. So God obviously has more say than US voters. The Soviet politburo had higher turnover than does the US congress.
2 party system also leads to other undesirable effects... ---- Election-methods mailing list - see http://electorama.com/em for list info
