Personally my favorite part of working with real publishers is editors. Having a development editor, technical editor, and a team of copy editors really helps making sure the book comes out polished. Additionally, I don't want to deal with all the layout work and the details of printing.

And, depending on the book, yes the distributor the publisher has can be very helpful for sales. It's nice to be able to grab your book off the shelf at Barnes and Noble (and, does lend a bit more credibility to your work).

All that said, if you're writing for purely economic reasons (which I would caution against regardless), you're probably going to make roughly the same if you self-publish for a small audience vs go with a traditional publisher for a larger audience, and if you can get a larger audience self-publishing then there will be no comparison.