This was a good bit I read on the Lightning connector and some of the thinking behind it:

http://brockerhoff.net/blog/2012/09/13/boom-2/

Assuming everything written there is true, then from my read of this, microUSB would never even have been considered. With a microUSB plug, the pins are apparently too small to carry the 2 amps of power that iPad charging would need. Some manufacturers have apparently hacked around this in various non-standardized ways. So, imagine if Apple puts that in the iPad (or some other future power-thirsty device). You can use any microUSB cable to sync or provide AC power, but only the Apple supplied adapter to actually charge the battery. You've completely negated the benefit of having the "standard" port, engendered customer confusion and loss of goodwill (how come my phone charger won't charge my iPad? It's the same port!), and gave up any benefits that would come from using your own superior connector design.

So, even if you disregard any ideas of wanting to control the accessory market or anything like that, there's absolutely no way Apple ever would have seriously considered microUSB just based on the power issue alone. (IMHO, of course)