I think its because graphics packs, databases, etc are usually “timeless” information that people will always need while the ebook segment is usually more topical.

That, and in the case of marketing ebooks, they are only good sellers until the “next big thing” comes along, then everybody jumps ship to the next big make free money idea.

I especially find it interesting that compilations and graphics tend to sell better over the long term. Of course, it might just be specific to your sample, but it’s interesting all the same.

Thanks for putting them together.