I'm thinking about the large size of new iPad graphics here. Anyone with an original iPad or iPad 2 that downloads a retina-updated app will also be getting @2x image resources. For graphically intensive apps this will be a huge burden. To a lesser extent it is a problem with iPhone 3GS apps downloading apps where just about all of them now have retina display graphics included too. These older devices will never use the @2x image resources so they do nothing but consume storage.
On AskDifferent a question was posted this morning that shows some scary figures for retina-updated apps. I haven't verified them but apps are getting drastically bigger. iMovie is the worst example, almost 6x the size!
The ultimate solution is vector graphics but in some cases it will be impractical and many developers updating existing apps will be wanting to just add new images and do the minimum to get an update out quickly.
How could this be done? The application documents directory is where an app can easily remove and discard files, but I believe there are limitations on the amount of data an app may install in documents? And in any other location the app can't remove files?
If this could be done then post-install the app would just delete the unused resources, keeping the specific resources it requires for the device it is on.
One problem I can see with this is that the Transfer Purchases from feature of iTunes would no longer be retrieving an app that is useful for other kinds of devices. An app using this feature might need to retain baseline graphics for both iPhone and iPad, and be capable of updating itself with retina versions (by download) if installed to another device.
