Ah, that makes sense.
It's one of the biggest ad networks on the internet. Someone being able to redirect all that traffic for their own purposes by modifying someone elses hosts files is quite the issue - considering how many websites have ads served by doubleclick.
By the way, doubleclick is run by Google - Microsoft tends to use their own advertising platform.
I would be curious to know if other high-profile sites are prevented from being redirected as well. I'd expect at least the Alexa top 50. Right now, we can justify each of those sites individually, but if it's ONLY those two sites, it's worth questioning.