I agree that obvious things don't really need a comment. But the problem of commenting only certain things as opposed to all things, is inconsistency across codebase. If new developer looks at the code and sees comments only at certain places, it might feel like the comments aren't trustworthy since there is no standard pattern. Also, I believe the term obvious itself is not objective (at the time of writing the code, most of the stuff are obvious)..
What do you all think ?