They don't need the money. I think they're doing it for the fans. The show must go on .... and all that. Working through greif is a great catharsis ... maybe they NEED to see the fans to put their old friend to rest?
There is great emotional drive in times of grief or bliss .... this tour might just be terrific. Anyone can cover the bass parts, so it will still souind like the Who. John was not that visible an image to the show. All eyes were on Pete and Roger.
I think it's a good decision.