I agree that we can do better about capturing donations after someone has downloaded or played. I think we held off adding anything because we wanted a flow for people to donate after they've played the game. Having a donation button on the download page could work though, if they happen to leave the download page open after they've played the game.
Regarding asking for a donation up-front, that will probably always be there. We try to make it very clear on the screen what the point of the dialog is, and it definitely helps nudge people into donating