I havent read the article but I would tend to agree that a blog can be a nice little earner but its all down to the type of blog IMHO.
Lets say you have a blog that is about your daily life rants, your posts are going to be of random topic so the ads being served are not really that well targetted. I noticed if you make a post about apples ads targeting that topic dont show until a day or two later - in some cases your apples post is already buried.
It also comes down to the type of visitor that comes onto your blog. If you visitor is a regular they usualy tend to come onto your blog to hear your latest rants or news and probably move onto read another of blog on their daily reading list. Where as if your visitor come in via the Search Engines there is a higher chance they will click an ad as they are seeking information.
In saying all that its from my own personal experience with a number of blogs that I have so people may have a totally different experience from Adsense on blogs.
What I do is select a topic that I have some knowledge on but that I also know has a high number of people searching on that topic. The second thing I aim for is to bring my visitors in via the Search Engines, they are the info seekers, the happy clickers
. If people become regulars via their blog reader or bookmarks etc then its a bonus (even if they dont click).
For one I wouldnt turn down my earnings made from blogs and maybe someday I'll just create one that allows me to retire with a year or two of blogging
If you are considering a blog find a topic that you know about, performs well from searches but also will probably have a high payout via Adsense.
Use least ads as possible, I tend to see that one banner ad and one text links ads work very well. The reason I do this is because I dont want low payout ads being served that a visitor might just happen to click on.
A blog might not see any income for the first couple of months so its a matter of keep plugging at it and get it ranked well in the Search Engines (thats the bread winner).