This is the route many webcomics take. Dare I say maybe even all. Plenty of comics have their printed editions kickstarted, or crowdfunded, or self-funded and release them through online stores or conventions.
There are comics I personally prefer to read online, but I also have my fair share of comics on my shelf that I've bought at conventions because I wanted a physical copy. Nimona and Hemlock are just a few favourites on my shelf. However, I don't always have the disposable income, but when I do I'm happy to do so.
Some may buy to support an artist, because they want to see more. Some may just genuinely want a physical copy (especially those of us who just like the feeling of books).
I could waste a lot of time making a list of all the comics that have both physical and web alternatives.