Brother None said:The fact that we understand aliens has been explained as a part of the TARDIS' telepathic field. As indepth an explanation as the Babelfish.
Let's not forget verisimilitude in these sci-fi comedy-action series. It doesn't have to make scientific sense, but things should still be explainable and plausible within the setting, which really isn't the case for Moffatt, who really doesn't care about any of Dr Who's established rules (even less so than RTD did)
NOPE, you are wrong, wrong, wrong, wrong!!!!

The Doctor is a Time Lord and can do things far above and beyond our meager understandings of the universe and physics. In fact, he has traveled beyond the universe and only a very few can even dare to claim they have even the tiniest amount of knowledge of what is and isn't possible there... or what was brought back.
What makes since to us in this timeline can easily be altered, thanks to the powers of TARDIS. We only know what the Doctor has chosen to share with us and who knows what things he did/will do/ is doing right this second... Heck, by the time I finish this we might find that Al Gore was elected president and never got around to inventing the Internet for us. LOL