Great post, jet. Thanks for the link to your price comparison.
We're still getting our email 'product' worked out, but for us the edge will be strategy. Sure, you can get cheap email delivery but knowing what to send and when is what makes the difference. We use the markup to subsidize the marketing consultation.
That's essentially what we do (using the markup as consultation fee), except that we focus on proving the additional services that most small businesses can't do (or afford to do) themselves; such as copy writing and graphic design.