1) Computers are, by design, a tool to lessen entropy. Computers sail through an Internet of chaos and disorder like icebreakers leaving a trail of ordered, aligned wreckage in their wake.
2) Any program or method employed by a computer to evaluate the "entropic value" of a string in the end means absolutely nothing except that it correlates to other virtual "entropic values" of other strings like it using purely ordered, metered and aligned correspondences of information bits.
3) Computers interacting or evaluating entropy in any way lessens the True Entropy of a system (or password or system of passwords).
Allowing a computer to determine entropy nessesarilly reduces it and using such a limited symbolic representation like a keyboard will soon not contain enough variables to adequately retain enough entropy to withstand faster, cooler processors. One method I see for future "password" usage uses the old Ars Memoria or Art of Memory, which I think is somewhat touched upon in xkcd's "correcthorsebatterystaple" method.
In short, letting PCs choose what is random or not is the exact opposite of how true randomness works. We wouldn't trust a randomness engine without knowing how that engine generated the seed of entropy injected to cascade information complexity but knowing how it is done obliterates it's entropic value. In real short, I'm really stoned and I don't know what I'm talking about anymore and this post is too long and boring...I'm hungry dammit.