Is it bad to leave his parents off the invite?

My parents are paying so their names are on it. His are not paying so they are not listed. I based this decision off of what I read elsewhere and I believe I am following etiquette rules.

I am the mother of a soon to be groom. My husband and I received the wedding invitation in the mail with very little conversation beforehand. It said our sons name on the invitation, of course, but did not say the son of _______________________. I am trying very hard not to be offended. From a mother's perspective a woman wants to at least be acknowledged for all of her hard work and efforts in making her son into the man that he is. A lot of the comments on this post are very helpful, thanks.