Having had both cats and dogs, I would say that there the trainability of both relates more to what they evolved from than from how smart they are. Personally, I'd put them both at about the same level. I've seen very smart cats (have one now that can turn light switches on and off and open doors on her own) and very smart dogs (had one that "rescued" the little girl next door's doll carriage before it rolled into the street). And I've seen not-so-smart examples of either.
Cats pretty much evolved from solitary rodent hunters. Dogs evolved from pack hunters. So dogs are used to having a social structure with a chain of command. Cats are used to operating independently. So, for a dog, it's a hop-skip-and-a jump to put you at the top of the pack. For cats, it's more about what they need. Not to say that cats don't establish a pecking order or social dominance or social niches.
I guess it still does come back to cats resemble women and dogs resemble men. Its still easier for a domesticated dogs master to train them because they have developed that willingness to follow and submit to, the person who has the treats.