Well, I may be wrong but this is how I've always looked at it. its not absolute necessary meaning your bike will not explode if its not done. But it is a good idea and highly recommended to be done.

One, you're already in the bike that far and have the cylinder off.
Two, Usually your rings and piston wear to the cylinder wall. This means that when you replace them you want the cylinder wall to be honed just to make sure that there are not any odd surfaces for the new rings to wear to.
Three, It is always possible that your new rings will not fit 100% like they are supposed to, unless you have it honed.

And hones are cheap. I got a local bike shop to hone my cylinder for $15..

I'm sure someone will correct me if I am wrong though.

Alright sweet. Thanks guys.