How much time has passed since the sale? While I agree with what others have said, in that you should really judge them based on the results, I do also agree with you that post closing thank yous and follow-ups are good practice and common courtesy. Unfortunately, common courtesy can be lacking from many aspects of our lives these days, and this can be true on all sides of a real estate transaction. If it hasn't been too long since the sale, maybe they'll reach out to you in another way, aside from a closing gift.
If I were you, I'd place the most importance on their overall performance. They obviously got the home sold quickly, so how did you feel about them in terms of communication, professionalism, knowledge, etc? If you were happy with all of this, and certainly you are happy with the results, I wouldn't place much importance on anything else.