Passphrasing is weaker because it still leaves you vulnerable to dictionary attack.
Also, if your router and gear supports WPA-AES, it's no more difficult to setup than WEP, but is far more secure. Granted, the locked door analogy is absolutely correct as most people aren't going to go through the trouble to hack your network when som many open ones are available, but the FBI has cracked WEP networks in under 3 minutes using packet injection... while they claim that WPA hasn't been cracked yet. If the setup is just as easy, why not go the secure route?
There are free 128 bit key generators on the net. It's just a matter of generate, copy, and paste to have ridiculously strong encryption. The weakest part of your network becomes the router password, which hopefully isn't 'cat.'