Interesting, that could well be it. Languages I pick up very easily (in rough order): C, C++, PHP, C#, Java, Scala, Perl, Python, Ruby, Javascript, Lisp. Haskell is definitely one that gives me trouble as well. It's not the functional aspects: I've no trouble writing recursive descent parsers and the like in C++. I can't stand the parentheses, but I can understand and reason with Lisp.
I think in Haskell's case, it's just doing too much with too little. Like how they can implement quicksort in three short lines of code, and to me it's just so much to unroll in my head at once; but it's hard to be sure for obvious reasons.
All the languages you list maybe except for Lisp are basically the same. They are all imperative, some of them are object orientated. If you understand e.g. C++, you should understand any of the others with not much effort. Really different languages would be Haskell, Prolog and maybe APL. Or recursive (hence Turing complete) SQL queries.
I've been using Haskell for a few months now, and quicksort has become trivial to read. Although, I agree that knowledge of other programming languages barely transfers to Haskell. I think being very different is the main factor that restrains Haskell's growth. It says a lot that Haskell's popularity grows anyway.
I think in Haskell's case, it's just doing too much with too little. Like how they can implement quicksort in three short lines of code, and to me it's just so much to unroll in my head at once; but it's hard to be sure for obvious reasons.