Regardless of how it starts out, it seems that everyone is trying to figure out how to earn a buck on the web. Some folks ask me to help them build their website simply for fun, or the learning experience. Others start out building a web site as an income producing vehicle. I've been involved in many business ventures over the years, as an owner, manager, sales person, employee. I know of a lot of folks who make a few bucks off of a hobby, and other folks who work out of their house that pull down 6 digit incomes.
Websites are no different that any other business.
There's a few web sites out there that started out small, and are now pulling down big bucks, but that's the exception not the rule. It's not different than the millions of sales people in the world, there's quite a few working hard to make ends meet, and a small handful pulling down six and seven digit incomes. With a website, like a business, there will many determining factors to success. Do you have any real gauge of number of visitors you'll be able to draw, or how much does each visitor spend. Keep in mind simply building a website, or even building a website that generates heavy traffic, is any guarantee you'll earn a dime.