Yes and no. There are a lot of webcomic creators (myself included) attempting to do this for better or worse.
Yes, intermediaries take a cut of our proceeds, but in exchange they provide a certain level of convenience - I can own a $300+ button-making machine and sell my own buttons as they're ordered online / at conventions, or I can focus on just making buttons for conventions (when I can make a reasonable estimate of how much I need at that time, hence can make a bunch at once on someone else's machine for just the cost of the buttons) and leave the online work to Zazzle, which does (in addition to buttons), several other items I can make and sell using the same images, with no upfront costs.
At no time do I give up my copyrights to these images, so I can use them elsewhere, and if it doesn't work out, I haven't lost any money in the process.
Ideally, other POD systems or small-scale operations like Amazon's recent offerings make it EASIER for me to stand alone with marketing my work, by reducing the cost and issues with fulfillment.
A LOT of these creator-run operations don't have the time or money to run marketing research to decide if it's a good idea to make a hundred shirts, or X number of books (The cost per unit goes down as you order more, but at the same time, if it doesn't sell, it's just wasted product) so the solution requires a system that carries its own burden for the creator to reduce waste as much as possible.
We COULD do work without them... but then the game goes to the ones already big enough to handle their own fulfillment, or the ones foolish enough to invest lots of money in it before doing their homework. I'd rather have 'em than not.