The $78 million number actually is far smaller than I would have expected, given the size of the country plus overseas buyers. It is a pittance in contribution of revenue to the USPS's budget as a whole. It is also a gross sales number and it would be interesting to know what the net margin is.
If you want to be truly depressed regarding all things USPS, read their financials, which are here.
http://about.usps.com/who-we-are/fi.../welcome.htmInterestingly, the 2014 10-K (annual report) does not use the words "philatelic" or "collector" anywhere. We are not a significant enough segment to report. The $78 million in philatelic sales isn't broken out separately.