By default Adblock Plus will allow some "approved" ads. You do have the option to not allow the "approved ads".
See info here: Allowing acceptable ads in Adblock Plus
Copied from above link....
Starting with Adblock Plus 2.0 you can allow some of the advertising that is considered not annoying. By doing this you support websites that rely on advertising but choose to do it in a non-intrusive way. And you give these websites an advantage over their competition which encourages other websites to use non-intrusive advertising as well. In the long term the web will become a better place for everybody, not only Adblock Plus users. Without this feature we run the danger that increasing Adblock Plus usage will make small websites unsustainable.
Why is this feature enabled by default?
Because that's unfortunately the only way to reach the goals outlined above. If we ask users to enable this feature then most of them won't do it — simply because they never change any settings unless absolutely necessary. However, advertisers will only be interested in switching to better ways of advertising if the majority of Adblock Plus users has this feature enabled.
But I hate all ads!
No problem, you can disable this feature at any time. Click the Adblock Plus icon and choose "Filter Preferences" from the menu. Uncheck "Allow non-intrusive advertising" and you are done.
Will all "acceptable" ads be unblocked?
No. Unfortunately, it isn't technically possible to recognize "acceptable" ads automatically. We have agreements with some websites and advertisers that only advertising matching our criteria will be used, their ads will be unblocked then. We hope to grow our list significantly over time.
EDIT: I wanted to add that I have contributed a few bucks to them. I like to think that many others who can have contributed, too.
Edited by buddy215, 29 June 2013 - 08:48 PM.