I agree, seats, specifically Y seats are not all the same.

But that's why it's typically on a first come first choice basis. Now, certain seats, such as the ones on exit rows, can be a little bit more special given the extra legroom, thus I think it makes sense, on a business perspective, that access to them should be restricted to the airlines frequent fliers, for free.

It's still a coach seat after all and the ability to access these seats is one of the ever decreasing benefits that an airline could provide its loyal customers.