How can conservatives say Hitler was a leftist/socialist?

[Senator Incitatus]

I'm curious as to whether this phenomenon is at all common outside the United States (and Canada).

Seems to me that nations which have had basically exclusively liberal histories, like the United States, would tend to view both fascism and communism as equally "other." Liberals have a tendency to lump all "other" political thought together as "tyranny," which explains why the American "right" — which is really a liberal traditionalist movement — makes this claim.

Also, Hitler is synonymous with "bad" and it's easy to just compare your enemies to the guy everyone agrees is bad.