No, actually, you're wrong. You cannot back up your saves to a flash drive. Saves are locked to user accounts, and if your PS3s HDD dies and you need to replace it, you'll be using a different user account even if you give the account the same name as before. All the games you copied out to an USB drive will therefore not work at all on your new user account. Sure, you can copy it back and forth and whatever you want, but when you start the game, the game will tell you "this save file is for a different user account, smurf you and good bye".

So the only way to take a backup of a 2 MB save file is to take a complete backup of your PS3. My PS3 currently has 200 GB on it. Backing up 200 GB is not nearly as convenient as backing up 2 MB. I don't even have an external drive witht hat much space, and if I did, I wouldn't want to spend it on backing up 199,9 GB that I don't need a backup of.