Shipping an iMac cost nothing -- yes the boats guzzle up fuel like crazy, but 400 20' containers can take a massive load. The cost on an individual computer, shoe or pillow is essentially nothing.
Apple airships pretty much everything. If you settle for transit by boat, you're going to have at least 4 weeks between leaving the factory and being in someones hands. Apple pushes to hold stock less than 1 week.
Shipping times are actually longer now than they were 5 years ago. Right before the financial crisis, shipping companies built up their fleets significantly and built "super ships" with huge capacity only to be met by diminished business just years later. As a result, they've deliberately slowed down their ships to cycle in more of their otherwise-would-be-idle ships.
