I think digital sales are essential. We would be at the mercy of the publisher/console manufacture for the numbers. Some are rather open about it - as we know Minecraft has sold millions digitally on the Xbox 360 - but on the download link I just looked at it only has just under 100,000 (but that may just be people that rate it.)
I think digital sales will be the ones to watch. You can't run out of a launch game if it's digital. It's easier to fix things, uses less resources to distribute, etc.
I think physical copies will go the way of books, movies, DVD's, Music, CD's and records. There will still be sum sales, but the vast majority will be like a phone app - all digital.