...To be fair, for Derpy's original voice, voice actress Tabitha St. Germain thought she was a boy, and based her voice on the kid of one of her neighbors. Even if it does seem like a bit of a lower-quality rush-job, I can at least approve of making the voice more feminine, since I didn't think think the previous voice really fit. The cheering at the end sounded spot on.
Changing 'Now careful, Derpy...' to just a flat 'Now careful...', on the other hand, is much more disappointing, since it was really the first major nod to the fandom that we got... But that could still at least be a copyright thing, rather than a political correctness thing.
...Unless someone at Hasbro actually went on record elaborating things, anyway.