Much as I think 4e is perfectly ginchy, the lack of mules probably has something to do with a design decision I don't personally agree with -- spending gold on magic. Once you have something clearly superior to spend gold on, unless you have some really roleplay-heavy players, magic is the best thing to spend your money on. And that gets kind of tragic. I prefer games where cold hard coin is something you're encouraged to spend on luxuries: spyglasses, sailing ships, owning your own property (and improving it), ale and whores. I really prefer having a "magic economy" that's divorced from gold, because then players feel that a fine standard of living is what gold is for, and act accordingly. It was a problem in 3e, and it's still one today.
Now that we've got the whole "alternate rewards for magic items" set up, there's really such an opportunity. Let people use alternate rewards as the basis for a separate economy of power-ups, and then figure out a gold-just-for-luxuries economy. Probably won't happen, but ah well, one can dream.