I think the issue is not that anyone is comparing them as equals (as Google isn't a social network, and Facebook isn't a search engine), but that Facebook can t

I think the issue is not that anyone is comparing them as equals (as Google isn't a social network, and Facebook isn't a search engine), but that Facebook can take the place of some specific Google searches. Consider searching for a restaurant in the area you're in. With Facebook, you have the choice of asking your friends (whom you trust), OR you can go wading into Google's search results and manually sort through the SEO'd "111-best-restaurant-review-site.com"-style garbage that populates the first few search result pages.