Over at ICv2 is an interesting opinion piece about the lack of digital sales data:
I was just wandering where the sales figures for digital comics and manga are. There is all kinds of sales data for printed comics, but no sales data for digital comic sales. Might that be because the publishers do not wish to share that information with the brick and mortar stores? Hmmmmm, I wonder why that is? I wonder if the increase in digital comic sales reflects the decrease in printed comic sales? Am I the only retailer asking this question? If you think I sound paranoid, then where are the sales figures for digital comic sales?
Check the whole thing out here