Look at the entire tax infrastructure - H&R Block and all those accountants basically doing a make work job, that could be eliminated by simplifying the tax structure.
The tax code is complicated because it's layer upon layer of incentives and disincentives and hacks and amendments and loopholes and counter-loopholes built up over decades. It evolved into its current state, it wasn't built this way.
Why Can’t the I.R.S. Help Fill in the Blanks? http://www.nytimes.com/2010/01/24/business/24digi.html?_r=1
Intuit's end-run http://articles.latimes.com/2010/jul/21/opinion/la-oe-ventry...