This is no surprise. Spam falls into about three catagories
1) Scams/false products
2)Actual products (porn/dvdcopy/telezapper/software/etc)
3)Affiliate programs
Most companies prohibit spamming their affiliate programs, but they don't do anything to stop it. Affiliate program spamming has been going on since the first one was created, it's not going anywhere. there's too much of it for the companies to hire someone to police it.
Not all ISP's profit from spam. I get at least 10 emails a day with 100k or larger attachments (one way spammers get around filters, they email you a giant image file with the ad on it). That's roughly 1mb a day incoming for my email account only. There's people on my ISP that get WAY more spam then I do.