Good point, ..., that could be a compensation preference the user sets when signing up. I was thinking of this as something that gets someone to try mining, without having to learn anything. Being compensated in PayPal is something familiar.
But there's no reason to not allow, if not encourage, the user to opt for compensation in bitcoins.
Indeed, a choice seems to make sense.
I could imagine someone thinking "Pff, why bother for fake money", but then "Oh, I can get 'real' money" and then, "Cool, I has money, what exactly is this all about?"