This restriction seems ridiculous to me. I mean, why? Could apps have problems opening apps from the Trash? That's the only reason I can think of. Can I test that? In fact, yes.
What would I expect to happen when I double-clicked on Picture 1.png? Open in Preview.app of course. Can I make that happen another way? Let's find out. First of all, where is the user's trash? That's easy, it's the .Trash directory in your home directory. Open Terminal and run ls -al to see the directory. Execute cd .Trash to get into the directory. Now run open "picture 1.png". Tada, it opens in Preview immediately, no problem. WTF? The .Trash directory is a hidden directory in UNIX (because of the dot prefix, works the same for files), could that be the reason for preventing opening files from the Trash, apps might not understand it? If that's true, Preview has no problem, and while there is a clear workaround to fixing this, from the user's perspective, this just makes no sense. Hopefully in Leopard...