The difference is, at the office it's part of your job, at home it is not. Helping your teammates is part of your job, helping your wife is not. And I bet you don't clock out to make a quick 5-minute break to help your wife 10 times a day ;)

If you are on salary - who cares? We aren't paid by the hour.

but that's working on work stuff, not personal stuff. You could make the 'but not my work' argument, but that's disingenuous I think.