I don't read the joke a day comics, but they are very popular on Tapastic, most of their biggest titles being joke a day webcomics and those are easier for them to promote as new readers can jump in at any point.
I publish two more serious comics, on ongoing superhero story and a Greek myth webcomic. I also read several - House of LSD, Codename Bathala, Demon Hunter Cain, SideChicks, Endstone, The Demon Archives; all pretty serious titles. The serious, ongoing comics. They are definitely out there, but Tapastic's emphasis on joke a day comics makes them a little tougher to find.