I don't think he has any moral obligation to donate the amount asked by Lodsys. Putting his head on the block like this is already helping a lot more than $3500 given to lawyers could.
He definitely doesn't have a moral obligation, but it is a fairly minimal number to help prove his intentions are genuine and not simply a strategy to save $3,500.
Also, he should stress the risk he is taking in defending his position since most readers will not have any idea how big it is.
