The iPad and AirPlay come so close to being perfect but for self imposed restrictions.
Fiddly text selection. What's wrong with cursor keys and block selection?
No SD card slot
No USB port or USB drive support
No access to the file system
No Flash support. I don't love flash but without it there are many URLs I can't access
AirPlay only works when apps support it. Why doesn't AirPlay simply show whatever is on the iPad screen?
Being forced to buy apps through the AppStore, unless you are prepared to JB. Granted this does allow some measure of quality control and automatic updates but at a price.
There was also no print support. That was quite silly. Even now I will have to buy one more printer than I need or want. Admittedly a no driver solution is a good idea.
With competition from Android devices perhaps Apple will be forced to lift it's game or see the iPad loose market share.