Let's stop the dogma and take it from someone who actually lives in LA. There SHOULDN'T BE "five times as many peds in V as there is in IV" because that would be disproportionate to the amount of people in LA and NY, and henceforth in LS and LC. The amount of people I see in LS is pretty much accurate to how many people I would typically see in LA, save for a few areas like the "del perro" promenade which should be alot more populated but that's just one area. The traffic in LS is also alot smoother than real life LA but that is understandable as its due to game limitations and the amount of vehicles on the screen at any given time is spectacular to begin with.
And yeah OP, the amount of detail is incredible. I always hated the unauthentic conversations that were had in GTA IV, it really broke immersion. In V, I can't tell you the amount of times I've walked past peds talking on their phone or to other people around them and actually having a realistic conversation.
I love the real conversations they have with eachother. Whether it's face to face or when one of them gets a phone call, it always sounds legit. Like you said, IV jus didn't sound right when it came to that sortve thing. I love this game and the little things they put an effort to put in the game.
Sure there might be some things they left out or forgot, but you can only do so much with current tech, ie; how much you can fit on a screen at one time. The fact they got a decent amount of traffic on parts of the freeways really floored me.
Overall they did a great job with this game. The pros greatly out way the cons.