The only way one would know what a person's economic interests are is actually talking to them, and I highly doubt that you've had those conversations. So, I'm guessing they're voting their best economic interests. It's just that they don't agree with what YOU think that their economic best interest should be. As for if you're not rich, you have no business voting republican, that's interesting. Based on who dominates where they send their money, it doesn't support your opinion.
Silicon Valley - democrats
Media - democrats
Entertainment/Sports - democrats
Wall Street - democrats
Link
Hedge Funds - democrats
Businesses - depending on the type of company, it's a mixed bag at best.
Link
Unions - democrats (from dues)
I know that there are plenty of rich people who vote republican, but your opinion that the democrat party is somehow the party of the common man is silly. I mean, don't republicans usually win the rural vote, and the democrats win the urban vote?