It is possible to memorize a 100 bit password. I once had a 1000 word poem memorized, and could write it down flawlessly from memory.
I agree that it's not worth memorizing, you should instead use a password database. But I still maintain my original point that there's no reason to assume that your password will be leaked eventually if you use a strong password.
I use a password database so I don't memorize most of my passwords.