It is possible, I have some of my apps on my iPad and iPhone (and some of them on an old iPod Touch). A backup doesn't contain the apps, just their contents and settings, so unless the actual apps are on your computer's iTunes then restoring to a backup won't copy them onto it.
You should be able to copy your apps (and other iTunes purchases so that you have copies of them and so that you can sync them either back to the same device if you ever need to restore it, or to other devices that you own) from the device that they are on to your computer's iTunes via File > Transfer Purchases (File > Devices > Transfer Purchases) and then sync them to the other devices (assuming that you have the relevant iOS version on them and the apps are compatible e.g. some apps are iPad-only, and some require full-phone capabilities so are iPhone-only). Or you can re-download them on your computer's iTunes and sync them or re-download them directly on the device that you want them on.
Re-downloading : http://support.apple.com/kb/HT2519
Syncing apps : http://support.apple.com/kb/HT1977 (if you have iTunes 11 on your comouter then you can enable the left-hand sidebar via option-command-S on a Mac, control-S on a PC - that might make the instructions on that page easier to follow)