Yeah I think using mobile data to play music is something you wouldn't want to do every day (although I do have a fixed IP at home so an easy connection to my 2Tb NAS rather than cloud storage), and if everybody was doing it the networks would quickly start throttling y'all.
It also wouldn't work for most peoples' commute in terms of connectivity. Rail lines are poorly covered for long stretches, and train wifi is always massively oversubscribed even before people start trying to stream music over it.
I guess if you carry a phone and an ipod you'll be alright with 16Gb, otherwise it seems an odd bottleneck for a flagship smartphone.