I think a good compromise would be something like this in the account signup (anthropomorphized):
Roku: Please enter your credit card so you can use the built in Roku app store.
User: No thanks.
Roku: Are you sure? If you don't link a card, you can't use our store, not even for free channels. This will limit you to only the Netflix, MLB and Amazon channels.
User: That's okay, I'd rather not.
Roku: Okay, we'll create your account now without a CC. Whenever you attempt to add a channel in the channel store, we'll send you a gentle reminder that you need to set up a CC to access all these wonderful things. (But we'll still let you look at them all!) Have fun with your new Roku!
-- GandK Labs
Check out Reversi! in the channel store!