Graphics and textures will be of amuch higher resolution which will mean more storage will be necessary. Worlds will be larger and more detailed. Gonna need bigger disc\'s. Multilayers on discs that can be accessed simultaneously would be an advantage, but I\'m not sure if blueray discs have this capability.
Storing all this content on the web and using bandwidth would be expensive for developers who have to store the data and maintain the 100\'s - 1000\'s of servers it would take to feed gamers. Also many gamers still do not have access to broadband or have fast enough broadband at this time to make the pursuit of a pure web based console feasilble.
We will however see lots of additional content available through the web this next gen.