I won't and don't pay my kids an allowance / wage / salary either, sure they get a treat now and then and helping out is a two way street because they need my help at times as well.
This is one good aspect to look at because you're setting the tone for your relationship with your kids when they're adults too.
Me and my brothers were expected to do a number of things around the farm on our own, and it was understood that there would be no money involved. My old man wouldn't even buy us our first vehicles, or gas or insurance.
Later on though, if one of us was having tough times, he was right there- quick to help us out. It didn't matter if it was money, or just him being there to back us up- I reaped the rewards of doing extra work for him when I was kid/teenager 20 times over when I became a young adult/adult.