That's the whole point. They know that social networks are not stable in the long run. They are now a new type of tech company, one with a huge pocket (in stock), and willing to make big bets with it.

Facebook is a tech rollup, and in my opinion, if they keep absorbing the most promising startups (and allow them to run independently), they could be a trillion dollar company with FB the social network making up less than 10% of that market value.