Well, that and the fact that the USPS is ludicrously cheap for what you get -- check out the comparison chart from earlier this year at Postal Sanity (http://postalsanity.com/2010/07/u-s-postal-rates-excel-in-international-comparison/).
That's... fascinating. Lulu's been around for years; it's a self-publishing and print-on-demand company. Nothing wrong with their website that I've ever heard anyone complain about (at least as far as security goes).
A list is only as strong as its weakest link. -- Don Knuth