Googleadds are not necessarily linked to your online activities.
You can see their priorities while picking an add for you like this:
1. They have enough data on your online activities that you have a trackingprofile that allows to send you ads fitting to said activities.
2. If they do not have any or enough data on your activities they will show an ad that fits the profile of the site you are watching (like goldfarming/powerleveling-services on WoW related sites).
3. If neither you nor the site have a fitting profile they will pick an ad from the unprofiled list (which in many cases are datingservices, medsellers, dubious creditsservices and such things). Or simply the ad for googlead itself.
So it might actually mean that some are simply not that easy to track in your activities as people who get more fitting ads.
And if you get a decent securityprogramm with an addblocker or a good standalone adblocker (carefull to not pick a "free" one of dubious websites you don' t know, that might be hidden malware) you won' t see anymore google-ads.