I routinely find myself astonished at how people think the online world should work. Everything should be free, don't charge for anything, let your competitors advertise in your space, ads are the devil, business plan is to make money through advertising... seriously people, the hell?
People respond to a story like this because it belies an attitude of weakness/protectionism from Facebook, not so much because of some kind of moral outrage about how things "should" be.
Facebook's exists solely on their website, and while some will try to argue that Facebook has by and large become "the web" for people, the point is that it's still their site, their rules, their game, and in turn you play by their rules. They don't hide this fact in the slightest.
It's simply good business for Facebook to block these ads.
The only exception, such as it is, would be that Google booted Copiepresse after that company sued them. They claim to be required to do so by court order, though Copiepresse disputes this. I haven't read the court order myself, so I don't know, but I can easily see it being badly worded.
If Google says "Let's play the game like gentlemen" I expect a gentlemens game from them.
Of course I'd love to see G+ beat FB. I hope that helps u to see, that I merely am against this kind of "under the belt hits". As long as G+ stays true to it's word of "don't be evil" I absolutely support them over FB.
This is business, plain and simple.
The comparison would be if Google did not allow Facebook to advertise in Google. Either way, I think it's hard to compare their advertising spaces due to their very different natures.