You are not alone - I am a preservationist as well. No dogears, no underlines, no notes jotted in the margins. A have an old SIMM that I use for a bookmark, but lately I have been using a really cool booklight called the lightwedge. Otherwise, apart from a little wear around the edges and spine (unavoidable), it remains in great shape.

I think it is just a different way of absorbing the information in the book. Some need to absorb it, comment, jot, underline, etc. in and around the text, making their thoughts part of the text, surrounding it. Others draw the words in, doing this processing in the mind.