When kids make a fuss a lot of parents I see around my area, it's not necessarily world-wide, just what I've observed, they can only react in two ways. They either get angry and slap the kid and cause a scene, or capitulate to shut the kid up and the kid ends up playing some gorey game they shouldn't have access to. and then everyone wonders why these kids end up with no job, no prospects, more kids that GCSE's. It's not the fault of the game, it's a product, it's to be used responsibly. It's the fault of the parents who don't give a crap.
As for the store staff, I agree that they need to be more responsible, but most of them in this area at least get paid minimum wage and get treated like crap by everyone when they sell out of the latest killer app. They become so jaded by it all that they stop giving a shit, for the most part. I do know a couple of exceptions that have even ID'd me before even though they all know I'm old enough it's still procedure, etc. But the majority of the staff are in the same place as the parents. Life isn't what they wanted it to be and they can't cope so they just give up. It's the biggest problem in modern western society, IMHO. People hold themselves up against celebrities and multi-millionaire tramps famous for being tramps (Paris Hilton, Kim Kardashian, etc) and when life doesn't bring them any of it they don't have the spirit to just get on with it. Everyone expects the easy life and nobody actually gets it. Whereas I've been through hell and back on my journey so far, pretty much any minor improvement to my life can be a game-changer to me.
Your observation is very apt, I studied about it during my psychology course and it has to do with the very simple mechanism of rewards and punishments, although it may not seem to do so on first glance.
What happens mentally is that the child is subconciously checking its footing with the parent to see how far it can go in negotiations. The parents are afraid of the social stigma of
"causing a racket in a store" and for the sake of keeping up appearances, they bend to the child's wishes wheras from the start, the answer should just be
"No." and if the fuss continues, they should finish their shopping quickly and leave the store.
Bending to the crocodile tears
teaches the child that goals can be quickly achieved by means of aggression, be it mental such as yelling or physical like tugging at the sleeve etc. This is a
"reward" which instills aggressive behavior and the more often it occurs the more frequent and elaborate will be the scenes as time goes by. It looks innocent enough, but it's actually a
very effective way to teach a child that by being aggressive, it can obtain immediate real life benefits.
The parent should make it clear that no negotiations are about to take place and that his/her decision is final - instead, they engage in banter with the child which informs the child that it has equal footing, which it shouldn't have since the parent is supposed to be a figure of authority.
Of course this is a complex subject and I'm only touching the tip of the ice berg, not to mention that I'm not exactly an authority on the subject, but long story short, by allowing this to happen, you're
"tickling the kid's Pavlov" so to speak.