In this case it's malware injecting ads, not Google
Will inevitably happen though--vigilance can't be constant
I think it's malware that hijacks your search by injecting their affiliate/cse-id. Any click on ads will get them a kickback and it's in their interest to get the CTR as high as possible and they can accomplish that by removing all the indicators (or as much as they can) that these are ads.
Oh man, that would suck. Even now when I blindly open link from google to download, for example 7zip I always double check the url I landed on just in case.
Would be so easy to fuck up so many computers with this method.