Only one of the SpaceX Falcon 9 boosters stayed afloat after a gentle touchdown (they weren't quite sure what to do with it, with a persistent rumor the Air Force used it for target practice); there's usually enough propellant left to make it kaboom when it tips into the water. I'd also imagine they didn't put a boat close to the landing target this time around for safety reasons.

I'm hoping they had a reconnaisance aircraft out there, though.