This site, like most, use countermeasures to ensure that advertisements are displayed. This is an ad supported web site.
PHP runs on the server so the adblock plug-in cannot find it. The blockers have no chance.
By checking to see if a given advertisement container is modified, then a blocker is detected. The modification is the key to identifying adblock use. Using multiple randomized checks defeat all adblock users.
Most recently we have seen advertisers begin to offers some web sites tools to secure sites from adblock users. PHP scrips are easily included with most web sites and this seems to be the best solution. Many site developers are of limited skill so having advertisers lend a helping hand is very welcome news.