Why doesn't iPhone/iPod touch have wi-fi timeout to increase battery life?

jailbreak then get sbsettings from cydia, with this you can slide your finger across the status bar and access a bunch of customizable toggle switches.

I use the Toggles: wi-fi, 3g, ipod, processes, volume, brightness, ssh, and auto-lock. It is a very useful jailbreak app.

Note: when you lock the phone it disconnects from wireless...

because having to reconnect it would be as equally annoying?