Both AirPlay and AirPrint must detect compatible devices on the network. There's a handful of HP printers that are directly compatible without running third-party software on a Mac or PC to share other printers. AirPlay compatible devices right now are pretty much the new model Apple TV. No compatible device on your wifi network, the options won't show up. AirPlay for example, if an Apple TV is detected, will show up as a little icon by the volume control in the iPod app on your iPad.
In my experience, although better in 4.3, AirPlay detecting my Apple TV can be a little wonky. Sometimes I have to wake up the Apple TV first, or wait a bit after starting the iPad iPod app.