I think the main argument against this is the risk of running out of battery while you are using the computer. Forcing the user to stop using the mouse to charge is not very great.

That being said, I think Apple's (or Ive's) justification for the port on the bottom would come from the design issues with a front-facing port (asymmetry), and I guess for them the trade-off is worth it. It probably is for me, too.