Why is the American classification of political ideology so different from the rest of the world?

[Call of the Wilde]

In most of the world, you have three kinds of parties:
Liberal = limited government, free markets, pro-business, more social rights (abortion, gay marriage)
Conservative = traditional, favors ultra-rich, religious themes, supports landholders
Socialist= big government, large social welfare programs, working class support

In the U.S., we called the Democrats liberal and the Republicans conservative. But by these definitions, aren't BOTH of our parties liberal? They just happen to focus on different kinds of liberalism (economic or social.)

Eh?