Was there ever reasoning presented for the size of a satoshi (i.e., the minimum amount of bitcoin that can be transacted)? If not, what are the prevailing critiques and concerns of that design choice?
Like most of these internal choices in the Bitcoin system, it's not really explained by the author and can't be easily changed even if anybody had a strong objection to it. Internally all values are 64 bit integers, and just displayed to the user as value / 1e8. 



The original wxBitcoin releases displayed two decimal places of precision.