The iPad can't do a right-click for two reasons:
1. Right-clicks were less useful on the iPhone (and the iPad is just a big iPhone with the same interface).
2. Steve Jobs doesn't think we need a right click. Apple users waited almost two decades to be granted right-click privileges on a Mac computer.
A right-click could be an extension a press and hold gesture used with copy / paste today more options on the pop up menu (but honestly this method is a bit slow for people who want to invoke actions FAST!). Or it could be a proper two finger gesture like on a Mac trackpad. Either way, Apple wouldn't put one on a tablet as long as Steve Jobs is around. It's the best Apple Whitespace ever!
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Want more proof that Apple doesn't get right-click?
What does a two finger tap do on an Apple trackpad? You guessed it: Right click.
Do the same gesture with the new Apple Magic Mouse. Carefully rest your left finger on the mouse. Now click with your right finger without lifting your left finger.
What do you get? Wait for it... Left Click!