Saying thank you to the host

When ever we go out to dinner round someone's house, I always write a short email afterwards to say thanks.

The other day one of our friends made comment that last time they invited us over for dinner, we were the only couple who wrote after to say thanks. There were six other couples there that evening.

I then got thinking and it does appear that when we have had guests round not many of them do write and say thanks after the event.

What is the general view on this?