Per mailing list discussion. http://sourceforge.net/p/bitcoin/mailman/message/31640769/
"Advantages are obvious:
- having satoshi as 1/100 of the main unit is familiar to people like USD and cent
- All existing financial software can deal/store big numbers but typically only 2 decimals.
- Split could be linked with the introduction of the ISO code in one step."
It does not look like item 3 is feasible, but the first two are a strong rationale. Existing financial software trying to integrate bitcoin must convert decimal places, with all that entails (accounting and bitcoin numbers "look" different to outsider auditors).
Humans in general seem to deal with large numbers for small values (Yen) better than fractional ones (bitcoin).