I make decent money on my blogs and websites in addition to my hubs and working for clients via Elance and other freelancing sites. To make that much on a blog you have to be dedicated and consistent, a topic that is unique and not over-saturated, but not so niche that no one is looking for it either. It takes a lot of time and effort, but it can be done very easily. My oldest website earns about $450 per month in ad revenue, some of my smaller ones earn $50 to $100 or so per month.
The longer a site or blog is established, the more traffic and money you stand to make. You need to market, develop a following etc.