blocked sites

what i really dont understand is why some perfectly fine sites get blocked and other sites that arent very appropriate for school work are allowed.
the reason im writing this is because i recently found that tumblr had been blocked and at the same time i see peeeps going on games like "dont give up robot and dragon fable" both games although they cant be acessed by the internet people can put them on their USB and play their stupid non educational games to their hearts content.
Also the school has blocked hotmail which on many ocasions i have sent homework to myself and i havent been able to acess it from school
i think the system should be reveiwed to stop the USB games from being accessed and other non harmful sites to be acepted

the mosrt addictive game in the world

MINECRAFT
MINECRAFT
MINECRAFT
when you are asleep you think of MINECRAFT
when you dont have it you would give your grandma to get it
MINECRAFT has the potencial to be huge its only in its alpha stage prebeta (still in development) and there are a heap of people playing it. you should try it it probs as addictive as somke illegal drug