Re: What if it was ditched and sunk intact?
I thought that might stir up a few people ;-)
Re: the Hudson River incident: as others have pointed out, it was on a calm inland waterway, not the open ocean. And that was hailed as a feat of extraordinary piloting.
And no, an A320 is not a large jet (Airbus describes it as "The founding member of the Airbus single-aisle Family" (http://www.airbus.com/aircraftfamilies/passengeraircraft/a320family/a320/)).
As for the list of water landings (http://en.wikipedia.org/wiki/Water_landing#Commercial_aircraft), have a look at the aircraft types and the outcomes. Most of them are much smaller aircraft, and the outcomes were not generally very good.
Interestingly that same Wiki page claims that "The FAA does not require commercial pilots to train to ditch".
Getting back to MH370, you could argue that a pilot who was prepared for ditching and had not run out of fuel, had not lost one or more engines and was not flying in foul weather could do it. Possibly, but he'd still be trying to land upwards of 140 tonnes of aircraft at 250km/r. In the dark.