To answer the OP's question, I'd say this is not important at all, and is merely an expression of a fitting philosophy rather than some gold standard that needs to be met in order to ride a bicycle, for example, like your feet need to be able to reach the pedals when sitting on the saddle. That's important. Being able to hold your torso in the hoods grip position without using your hands is not.

Exhibit A: I've never tried it exactly, but I'm pretty sure I can't, yet it doesn't stop me from riding happily for hours at a stretch, and with some pretty decent power.

Alternatively, if you want to ride a bike like you would sit in a chair, then yes, this is important!