SASless, the reason may be that the birds entered the engine of the airliner, while they apparently didn't enter the engine of the S76. They were producing power at impact, according to the NTSB. Those on the airliner weren't, which is why it went into the Hudson River. It's much harder for something to get into an S76 engine than a pure jet engine, because of the design differences. Not impossible, but harder.