It's cheaper to get the $100 upgrade to 64G. Bigger data plans get expensive in a hurry here. Given that you're using a phone for at least a couple of years, paying an extra $40/month for the big data plan vs. $100 up front for enough storage not to need the upgrade just doesn't make sense.
Of course if Apple didn't have to skimp so badly on the base phone the upgrade wouldn't be necessary. Shame so many Android phones are also 16GB. My experience with using microSD cards for more storage is a bit less than spectacular as well with so many of the stupid cards dying suddenly and without warning.
Also apps using sd for storage is on an app by app basis. So say if Google turns that off for Play Music - as it seems they just did - well, now I have to cancel my subscription for that service and find something else to use my 64gb sd for. ffs.
Of course if Apple didn't have to skimp so badly on the base phone the upgrade wouldn't be necessary. Shame so many Android phones are also 16GB. My experience with using microSD cards for more storage is a bit less than spectacular as well with so many of the stupid cards dying suddenly and without warning.