On my PlayBook and my BB device I have the same BlackBerry ID.
My gf's device and her PlayBook have another ID. You can add up to 5 different devices to the same BlackBerry ID. http://docs.blackberry.com/en/smartp...340-001-US.pdf KB28543-Expectations when using the same BlackBerry ID on multiple devices
If you are talking about a PlayBook and a BlackBerry device, then yes, you can use the same ID. The reason you can use the same apps on all your iOS devices is probably because you used the same itunes account for all those devices.