On a different note I wish the PS3 would adopt the 360's way of installing the entire game to the hard drive. I can't think that either Sony or Microsoft will stick an SSD in their next generation console but having a 500 gb hard drive shouldn't be too costly.
A disk is a lot cheaper to stamp and print than flash or some type of ROM would be.
But yea, I think you're right that the optical disks will still end up being cheaper.
1. Everyone has a fast internet connection to the point where downloading a full BluRay disc of content (~25GB) is a non-issue.
2. Everyone has an Internet connection where downloading up to 25GB of content for a single game will not go over their transfer caps, possibly incurring usurious overage charges.
3. Everyone that will buy a Playstation 4 will be well-off enough that they don't need to resell their games after they have played them in order to afford the next game that they want to play (effectively only paying the difference between the original cost and the resale amount).
Consider also that we're talking 2013 onwards. Connections continue to improve.
Unless we get either reform on who can lay fiber or get some national fiber channel program in the states, only big cities stand a chance of seeing meaningful increases in bandwidth this decade.