If you've discussed it openly and plainly, and he understands you feel underappreciated and hasn't changed as a result, then... he's telling you making you feel appreciated isn't important to him. As you can see from the comments here, it is very possible for partners to show appreciation to each other. So you have a choice: maybe the lack of appreciation is a flaw in your relationship you can live with because other positive aspects balance it out, and maybe it's not.