not the same volume
I agree, but why to buy on poloniex, if on mintpal cheaper?

idiots maybe !
those who bought in mintpal, can earn by selling in poloniex...
By the time you send them over to Poloniex the price will most likely rise, plus poloniex sales are usually slower than mint, due to the amount of volume.
thats the reason why you have to keep a positive balance in both of the exchanges...