If people were perfectly rational, this might be the case, but I don't think receiving a statement has the same emotional impact, and is not as attention-grabbing and drawn-out, as going through the process of preparing a return - especially if, as for many people, you get a refund.

My guess is that relatively few people, of those who currently prepare their own returns, would invest as much time and effort into verifying an IRS-prepared return as they do in preparing one. I would also guess that a majority of swing voters prepare their own returns (I know, that's a fair amount of supposition on my part...)