It wasn't my list of civs, but I think I can guess an answer about why them:
Spain: Although it requires luck, their UA is insanely powerful, especially in the hands of a Human who can abuse it more. Also the Terrico (sp?) UU is pretty good. Finding an early natural wonder is likely to put you leaps and bounds ahead ofthe other humans if you can take proper advantage of it. And Sid help your human foes if you get something especially silly like starting your capital next to the barrier reef
Germany: Their spammable Landsknechts and lower maintainace costs are a bigger advantage against humans than against the AIs, because the humans your fighting can't spam units like the AI, so its much easier to achieve a crushing numerical supiriority against a human. You also have the potential to pull off a nice rush with converted barbarians