There's a difference b/w performance decrease and a program residing in memory.
See the previous example.
Look, this argument won't go anywhere. The point is jailbreaking your phone does NOT cause the perceived "lag" everyone is talking about; The applications you use, depending on what it is and how you use them, do. When you jailbreak, you're pretty much unlocking a closed door.
Either way, I'm happy I have the option of jailbraking. If you're happy with default, what's the real problem? The only issue I ever had was the misinformation being spread by some of your comments.
Nothing I can really do about that. You can continue saying "jailbreak = slow iPhone," just like some people think they download stuff off of CD's or the "internet is broken."