This is because the staff consider the bitcoin-XT currency to be an altcoin
They are correct. Bitcoin XT is not altcoin yet, but will be when hardfork of bitcoin will inevitably occur as a result of larger block size accepted in future!
Exactly. So why censor it now? Right now I can download the Bitcoin-Xt client, import my wallet from Bitcoin Core and spend my coins at merchants that use Bitcoin Core. So obviously isn't an altcoin client right now, its a usable Bitcoin client just like any other. Doesn't make sense to censor it now becuase it will become an altcoin client in the future.
They sensor it not because of the alt client but because of the alt coin! It makes perfect sense to me. Bitcoin XT is not Bitcoin!