I honestly don't think that it makes sense to separate activities into hobbies and into work.
One of the activities that I spent a lot of time with is Salsa dancing.
What kind of activity is Salsa?
Sure Salsa is fun.
Salsa has a lot of health benefits which in turn make me more productive in day to day living.
Salsa also provides a nice perspective on human physiology and you could call it field research. It has the potential to inspire academic ideas that I might publish (I'm studying bioinformatics).
I might write an android application that uses the accelerometer data to help you to dance on time and sell that application.
In a few years I might also start teaching dancing on the side.
If you have a blog and don't make money, you're a naive blogger.
There are a lot of reason to have a blog besides making money.
1) Having ideas that need an audience
2) Developing writing skills
3) Personal branding
I'm thinking of starting a blog because of #1
I think your friend is just being realistic. Blogging seems to be like the film industry a few people make a lot of money and everyone else makes a pittance.
The film industry pays the food of a lot of people while blogging pays the food of relatively few people.