Originally in RQ1/2 the random locations were described exactly as exploiting what was left open. There were rules for aimed shots at a penalty, but 'base' combat involved striking where the opponent left an opening. Hence the random location.
Granted in those days combat was a 12 second round and everyone but the most skilled only got 1 attack a round, so the attack roll (and indeed the entire combat round) was much more abstracted. The rolling for attack and parry may have felt like you were rolling for each swing and block, but in fact it represented the odds of landing a meaningful blow among potentially many blows, feints and parries over the course of a 12 second round. If you were determined to hit a particular you were less likely to land a blow in that 12 second time frame - hence the penalty for aimed shots.
As RosenMcStern points out historically leg hits were common, and from my (admittedly limited) experience with simulated combat legs are hit frequently as they are the harder to defend. It's not that I want to hit my opponents legs - I'd love to take his head off in one clean blow - it is that I can hit his legs, and would be a fool not too given the opportunity.