This might work in a game like Final Fantasy X, where battles are random encounters and you can prepare (to an extent) your arsenal and characters, but the idea of the Fallout universe is that anything can happen at any time with no choice but to fight with what you have. If a number of Deathclaws ambushes you in the middle of nowhere, with no one to pass by and lend a hand, you're screwed.
Well, thank God I can reload pretty fast, and OMG MY LAST MAGAZINE FELL ON THE GROUND!!11!11 ZOMG I'M DEAD.
And that's how that would go down for lower level characters. Besides, say that each enemy (Deathclaw) needs an ungodly amount of bullets to cripple a limb so you can run away. If you exhaust almost all of your magazine doing just that, and are being closed in by another enemy (Deathclaw) what then? It's just too inconvenient.
Well, thank God I can reload pretty fast, and OMG MY LAST MAGAZINE FELL ON THE GROUND!!11!11 ZOMG I'M DEAD.
And that's how that would go down for lower level characters. Besides, say that each enemy (Deathclaw) needs an ungodly amount of bullets to cripple a limb so you can run away. If you exhaust almost all of your magazine doing just that, and are being closed in by another enemy (Deathclaw) what then? It's just too inconvenient.
You can prepare more for combat in Fallout than you ever could in the Final Fantasy games. Until the last couple all the battles in the FF games were random encounters that literally exploded out of no where. In Fallout you can prepare you character every bit as much as you can in the FF games, and you have the added benefit of being able to see enemies coming from a distance. If you have a problem getting constantly ambushed in Fallout, you (A) Need to pay more attention (B) Invest more points in PER to get the red warning dots on your compass, or © Get a PC that can support a draw distance other than 0.
As for your last scenario - if you must expend most of your ammo just to cripple a deathclaw so you can flee, and another Deathclaw jumps you, the inconvenience of the reloading mechanic isn't going to matter one wit. You'll still be screwed.
The purpose of this theoretical mechanic that has been proposed is to require more planning on the player's part and less "running and gunning". Going back to your scenario, you would move cautiously (always) in case you ran into deathclaws, so you could see them before they saw you, and either quickly move away or plan ahead to be packing a ton of ammo for bear before you engaged.
That is the number one change to gameplay I see hardcoe Mode introducing - the fact that planning will now be necessary to avoid death. How many of us in FO3 entered into a subway tunnel or building or new area with no planning ahead or checking of our current health and supplies. I bet all of us, because caution wasn't necessary. Now we will have to be sure to count our bottles of water, our food supplies, check our ammo count and gun condition, and be sure to pack adequate healing supplies, and factor all that against how long and where we will be exploring. If that extended to ammo use and reloading, I wouldn't mind a bit.