^ Charles wasn't transferred, he just went back to doing his job as Jan (and Ryan's) replacement in New York. He was just subbing in as manager at Scranton until someone new could be hired. Wallace mentioned that he was still living in a hotel, after all.
Also, I don't get why David Wallace always gives Michael the benefit of the doubt and constantly puts up with Micheal's antics. I know that, apparently/somehow, Michael is a good sales person (and, by proxy, manager), but I cannot see any CEO giving what he gave to Michael so easily, regardless on how "good" he is.
Well, it was in Wallace's best interest to make the Michael Scott Paper Company go away as quickly as possible, since the Scranton Branch was starting to crap up under Charles on its own, and MSPC was leaching away their business. While they couldn't do it forever, they could definitely make it to the next earnings report, when, as Michael pointed out, all the investors would be very curious as to why DM's best-performing branch had suddenly taken a nosedive, and then things would snowball from there as investors started bailing out and going for the more consistently performing office-supply companies.
Getting Michael and his bizarre, controlled-chaos voodoo-savant management back was an added bonus, but the main reason Wallace caved was that they needed to reabsorb the customers Michael had poached.
I am a little curious if Michael is still going to answer to Charles or if they'll just make him directly accountable to Wallace to shut him up. Considering that none of this would've happened without Charles' attempts at micromanaging Michael (ignoring the rule about not fixing what isn't broken), it'd be the smart thing to do.