The data is from those sales-tracking firms.. you can also look up various analysts mix projections too if you wanted. You jumped context from 16GB to 32GB without prompting, 11.5GB useable is the useable space "now", the internal only preview version apple are playing with now I'm told is slightly bigger, so 11GB useable on the 16GB is not BS and I'm 99% sure you would not be so impolite and arrogant face to face, so why do it on a forum? it's just not needed and its not BS.
64GB for base is not absurd, firstly 64GB of NAND is now costing less than 16GB was at the launch of the 5.
Flash storage devices have grown from 64GB to 256GB as standard in some configs and by the same measure in the same time frame the MBAs RAM has gone from 2GB RAM 8GB as standard now.
Regardless of the fact everything else has grown by that same factor, i don't believe apple will go with 64GB. They will go with 32GB i'd wager, but that's because they are more bothered about "profit" than the customer and doing the right thing.