They didn't mention Facebook. Should they?
Twitter should be worried about facebook, after all twitter is a minor feature that can be grafted onto a whole bunch of other sites.
Facebook and twitter fans see facebook and twitter as the be-all-end-all, they don't realize that even though they're big they are not nearly as universal as google.
Search + ads = product, facebook / twitter / myspace / flavour of the day = fads / fashion.
Hard to do that when a rival website has a large proportion of that information inside their closed garden.
I don't think facebook is really something that is to be worried about except as an example of a broader problem.
If facebook were to die tomorrow I doubt there would be any big disturbances in the force (and twitter wouldn't even be noticed, except for some deflation of some egos). If google would die tomorrow morning the internet as we know it would grind to a halt. Search now drives the majority of traffic, plenty of people don't even know how to properly use the url bar any longer and it won't be long before it becomes optional and the search box is your main avenue to the web.
(Although I should say that I believe the sudden disappearance of facebook would be a pretty big deal, just not along the same lines as the disappearance of google would be.)
Facebook probably wishes they could target ads given all their demographic information. They probably want to be able to help users make decisions by leveraging their social graph, but I think in the here-and-now, and probably for the immediate future, that will not be the case.
I think it is silly to constantly worry about what everyone else is doing when it is substantially more fruitful to understand what you yourself should be doing.