My first thought is that it's a favor if someone asks you to help. Webster's defines favor as follows: To help, assist, support. Any act of generosity, goodwill etc.; as, he asked her to do him a favor.
Webster's definition took what I thought would be a simple answer and blurred the defining lines for me. So, the written definition is pretty broad, but I believe the social definition is it's a favor if someone askes or if you are doing it to help them. But, not to accuse, just for the record, I do not think it is a favor if someone is keeping score.
This brings to mind the following questions for me: Why does it matter whether or not it is a favor? Are these "favors" things that you would do for him anyway or are you doing them only because he has asked for your help? It seems there may be an underlying issue. For example, "favors can cut into time needed to take care of children, help with homework, etc.
Moms tend to get overloaded and often times the many, many tasks we complete daily do go unnoticed or are taken for granted. Are these favors for your husband taking time away the many duties/tasks you already have on your plate that keep the house and family functioning? Don't forget that it's okay to say, "No." :-)
Question: Would either of your definitons change if, just for a few days, you did not follow through when you "think of doing something for him"? Just a thought. Maybe, worth a try?
I hope this response has been helpful to you and your family.
P.S. After reading your clarification statement I would like to add the following:
One of the nicest things my husband does for me is he takes the kids outside when I want to take a nap or sleep in on the weekend. It ensures I get total rest rather than interupted sleep. Mr. "S" should give you a great big hug, kiss and thank you for thinking of him. An opportunity (which means a benefit to you) to "get out of the house" would have been more along the lines of leaving him to watch the kids and you go for a nice walk by yourself.