Well, Huffington Post reporter Amanda Terkel points out that he very well could have got the idea from a video game. Sounds a bit more plausible than a team of mysterious unnamed advisers. Maxis' Senior Producer Kip Katsarelis had this to say:
We encourage politicians to continue to look to innovative games like SimCity for inspiration for social and economic change," said Katsarelis. "While we at Maxis and Electronic Arts do not endorse any political candidates or their platforms, it's interesting to see GOP candidate Herman Cain propose a simplified tax system like one we designed for the video game SimCity 4.
The plan worked well in the virtual world, but without a god mode or the ability to turn disasters off, and an infinitely more complex society than that which is featured in a video game from 2003, can it hold up in the real world?