*shakes head at terrible voorhese retorts*
IMO, Fox, while rewarding for basic tech skill at LOW levels, gets very punishable later on if that's all he has. He's a featherweight, and his recovery, in agreement with CKit himself, can be quite punishable. Falco is a more extreme case of this, thanks to his worse recovery and higher reliance on not losing control of the match. Come to think of it, Fox and Falco both actually have amazing, high-speed attacks that are overlooked in the wake of the tech-skill mentality. I lost count of the number of times I've seen lists of what's good about Fox, and not seeing the U-smash until I dig through said list. Point: their tech isn't all they have. I know that's not what people said, so don't feel accused.
That being said, Marth does require a good degree of hard work to use that is mostly not tech-based. Prediction, learning to follow the opponent's DI, spacing, etc. are more of what Marth feeds off of, but he reaps great rewards once that's done properly. M2K against Shiz at RoM was a great example of that. A couple of spacing errors on Shiz's part and M2K just ripped him a new one.
Verdict: Agreed with Carl on difficulty of being good with Marth, but still don't think he's tougher to use than Fox at the highest levels. Just my $0.02.