Oh dear, this thread has been tp4'd
20mA on the spec sheet is just a reference value for the other parameters, like Vf and mcd etc.
For example a single rated Vf will be given that is only correct when pasing 20mA through the LED. There will also be a graph showing how Vf changes with different currents later in the datasheet (if it's a good one).
Put a bigger resistor in, or some other current control, and there's no problem running it at FAR less current. PWM could also be used to share current around over time.
Use decent LEDs, and that will still be plenty bright enough for backlighting. But of course some makers will still try and use the cheapest, or burn your eyes out
As for USB hubs etc, in practise I've found that some will trip out if you go over 500mA. That's why external drives usually come with that double-headed cable!