I sometimes do, because I much prefer reading the ebook. I also have preordered ebooks, and I obviously paid less than for the hardback in those cases. If the book is up to 9.99, I'll buy it if I want it enough, and if my local library does not have it. 12.99 is my absolute pain point, and it would have to be a darn good book for me to spend this kind of money on it.
With some books that are hot at the moment, I sometimes (very seldomly) purchase the dead tree version if it costs around the same as the ebook version, as much as I don't like reading on paper, so that I can donate the book to my local library after I read it. I wish there was a way for me to donate my already read ebooks to them....