There is virtually no land to speak of in that part of the world, so the plane had to have landed in the water.
It's not going to be an easy task recovering any debris, let alone ever be able to pinpoint the exact location of where the plane landed/crashed:
Authorities from Australia, China and France have said that satellite images have indicated objects floating in the search zone. The area is roughly consistent with a southern flight path calculated from “pings” emitted by equipment aboard Flight 370 and picked up by a satellite for more than seven hours after ground controllers lost contact with the plane.
The search for the aircraft’s fuselage and other bulky parts of the jet that probably sank to the bottom of the ocean is likely to be focused within a limited distance from the suspected flight path. But the search for floating debris, which investigators say will offer proof that the jet hit the water, is likely to be increasingly widespread.