I would think producing 50 gb+ flash for games would be prohibitively expensive compared to optical discs. Especially as they can continue to add layers to Blu-ray to add more storage space. As long as the disc read speeds are faster than the PS3's (2x) I think it's still an advantage.
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.
Disks are cheap, but disk drives are ~$80. (Consoles are sold at a loss, so this comes directly out of profits.) I don't know how big PS4 games will be, but flash storage could cost 25 cents per GB.
But yea, I think you're right that the optical disks will still end up being cheaper.
Why do we need physical media? I'd prefer to download them myself. I usually buy games in the Playstation store if they are available there. Yes, of course, this would mean that you probably can't sell your games after you're done with them, but that's not a big issue for me personally.
You're making several anecdotal assumptions based on your personal situation and extrapolating it to the entire target market for the Playstation 4:
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).
Not in rural, or even a lot of suburbian America. Telecom monopolies and all that. My mother has 300 kbps dsl, which she has had for a decade, and that is from Verzion, because they have an internet monopoly in her area.
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.
If the new games were made available at a cheaper price up front, I could live without the ability to trade in (at a price point of say €30 vs €50 currently). It might be viable as they aren't sharing a slice with the high street retailers.