Did I Discover a Major Hole in the Adblock Plus EasyList Filter?

It's normal. Some sites can register to AdBlock Plus if they think that theirs ads are "acceptable". It will thus be whitelisted in their database.

If you want to learn more: https://adblockplus.org/acceptable-ads

and also some are paying AdBlock Plus: http://arstechnica.com/business/2015/02/over-300-businesses-...