Commercial angle in blog posts

Anyone and everyone writes a blog post only to be read by others. But many writers strive to force it being read by others through gimmicks. One of the gimmicks I am personally against is the commercial angle.

Should every post have something to do with selling some service or product on the web? No, not necessary in my view. There are sites taht teach you how to improve hits, how to gather attraction from Indexing services like Google, how to cheat them by mnaipulating the title etc.

Are you for it? If yes why? If not why?