Even though there's hardly digital comics you can purchase, people still take the time to manually scan each comic as it comes out.
For manga, people even take the time to TRANSLATE it before they release it.
Just like anything else, piracy is based on demand, not convienence. People don't do all that work just because its easy, they do it because people want them.
The demand for ebook piracy may increase as people get more and more used to the idea of reading digital books, but wether or not a publisher decides to sell their books digitally would have no bearing on the chances of it getting pirated.
As a comic book collector, I love the pirated comic scans you can find on the web. why?
1) Simplicity in back issues. I have a physical copy of the entire Marvel comics run of Transformers, but going through my boxes, finding the books, unbagging them, reading them, rebagging them, putting them back in the boxes, etc, can be a pain. If I can download a PDF of the entire run, and read them on my computer, that's just great. Did it hurt anyone's sales? No, I already own them, I'm just happy for a different way to access the content.
2) Missed issues. This may seem like theft of a sale, but seriously? I'm a collector. I want the damned book. If I can't get my hands on the physical book for some reason, this is a great stop gap until one of my stores, offline and online, can get me a copy. Even if I'm never able to get the copy (some books skyrocket in price) at least it means I'm current with the storyline, and will continue to buy the title monthly. If I lose part of the storyline, often enough, I'll stop buying the book because I'm losing parts of the plot.
3) Recommended titles. If someone at a shop or show tells me "dude, you gotta check this out," I'm usually fair game. If it's still only 3 or 4 issues in, it's not a problem to buy all 3 or 4 issues. But if it's up to issue 12, or 25, or 50, it becomes unrealistic. If I can download the series and give it a shot, one of two things happen: I either dislike the book, and delete it, or I like the book, add all new issues to my weekly purchases, and then make an attempt to acquire as many of those back issues as I can. Remember, I'm a collector. That means I *WANT* the books.
Basically, I turn to comic scans to keep my interest, or gain my interest. When my interest is kept, I keep buying my weekly books, and both the publishers and the retailers are happy. When I become interested in something new, both the publishers and retailers enjoy my weekly purchases, and the retailer also enjoys additional purchases from their back issue stock. In my case, both the retailers and publishers are more likely to lose my money, had I no access to some of these scans. Is everyone like me? Unlikely, but I can't be the only one.