Actually, they do this already. I get e-mailed about once a week from Amazon asking me, "How would you rate <<Thing you bought a month ago>>?"

I frankly find it annoying. It's sad to say, but unless the item was either really good or really bad, I don't feel compelled to review it.

The other problem is most people probably review their things as soon as they get it. Very few go back and edit their reviews if the thing disintegrates six months later, with the net result that the product has overwhelmingly positive reviews despite having the durability of the Dead Sea Scrolls.