AWG I am 25, and do not plan on having kids..... EVER!
I wouldnt call those examples you have listed as "financial needs", more like "financial wants". But I guess if they have a set allowance, once they spend it, its gone. No coming to Mum and Dad to pay for their next phone recharge, they have to earn it. So I guess thats a decent system you have going there. If they are paying for online games, are they virtual reality games that require alot of time and effort like World Of Warcraft? Those type of games can create some very nasty habits and anti-sociable behaviour when played too long, they are actually quite adictive. I have seen it in ppl I know. However, they are fine in moderation. Even I still occasionally play a few online games too.
I guess hearing that a 14yr old gets $20 makes me feel old! I used to get $2 a week by helping work on the farm - help milk the cows, spray thistles, irrigating, cutting hay, etc... However whenever those jobs lasted longer than an hour, I'd get a little bit extra. But my parents made sure I never missed a football or cricket training session or game - so they counted that as part of my allowance.
And yes I got "thrashed" too