So, I found out accidentally that if you want to re-download de-listed apps and games from the phone store, you can go to "My Library" in the store and lots of apps that are no longer in the store can still be downloaded if you "own" them. For example, I downloaded 6Snap - Beta (doesn't work...) and Project Sunburst (the best Xbox WP7 game ever!) but the servers for it were sadly shut down.