Thus, I'm assuming that you were familiar with David's boasting at the beginning that he was personally responsible for getting Bush elected.
Reading that quote, I interpreted it as "consider what impact your vote might have on your job security" (from an economic policies standpoint, not as a threat of firing anyone who voted for the "wrong" candidate. He wouldn't have access to their voting record anyway. As threats go, it seems rather innocuous, and based in economic platforms not personal retribution).
Further to the point, though I find almost no character I can root for in the documentary, I'll point out that it was indeed the banking retraction and policies that led to their immediate loss of jobs (e.g. their customers no longer had access to cheap money, and thus, couldn't buy their product). It wasn't because the business owners were spending filthy amounts of money on personal homes and lifestyle. They wanted to expand, but couldn't...so in that regard, that email was perhaps accurate...no?