occasionally lurch forward after being shifted from drive to park?

You won't be able to remove the ignition key if the gear shift is in neutral, unless you do not have the shift interlock system.

When shifting to Park, did you ensure that the vehicle has come to a full stop?

The car is braked to a complete stop, and when my wife shifts from drive to park the car lurches forward. This has only happend four times over two or so months of driving.

When gear shift is in park, it should not lurch unles vehicle is not stationary. If you have this problem, then the ransmission has an internal fault and it is going to get worse. It is best to get it checked.

Note: I was told that the car is stull under warranty, but the dealer said that if there is no discernible problem they can seem, the tranny would have to be insoected, and that that cost would not be covered if it was not bad. He said the only way to tell is from computer codes, but this is a mechnical problem and I don't think there would be any such codes. He also said he was not aware of any such problem, but I found multiple instances on-line.

The dealer should not be taking the transmission apart without diagnosing and getting an understanding of what could be wrong. Mechanical faults that do not occur during driving are not likely to produce any codes.

What you need to do is to simulate the condition to the dealer and see what they have to say about it.

Since vehicle is still under warranty, make sure the complaint is recorded for future reference if required.