If you look at our industry it is panning out like a miniature biological ecosystem, with companies devouring other companies, some companies pivoting into different/new companies, big old companies being overthrown by smaller, newer, smarter ones.
Acqui-hiring is just one avenue for the evolution of technology to continue - and TBH, I may not agree with Facebook's policy but what they have achieved (virtually anyone that is "online" has a "Facebook") is remarkable with regards to the social graph and connecting people.