I don't see anything unethical about Steinberg offering incentives. It is still the customer's choice.
I think it is only unethical when the customer has no choice as Avid has done time and time again. Avid has successfully leveraged its market share to force many to stay with them. An example: OMF used to be over a $1000 option, with the "lite" versions, if you wanted to commit the heresy of porting to a different system. They set it up so that it wasn't "may the best DAW win". They are the 800 pound gorilla. I own Pro Tools now simply because I had no choice.
That being said, Pro Tools is not a bad system. Though I much prefer Nuendo.