The group, as an existing entity and with this defined as a group rule, has probably spent some thought on this. The will have their reasons for their decision. Expecting them to change their social contract with your arrival is, frankly speaking, pretentious.
If the guys are open to it you might start a new discussion on this topic, perhaps starting with the GM before you join the crew. At least you'll learn their reasons, even if you don't succeed in influencing the others.
The other way would be to try to reach an agreement that you might make you character(s) your own way. Propose to use the Character Manager and print out an extra version of the Power Cards for the DM so that he can easily reference it during play.
If one of your character's Powers is the same as that of another character in the group, but a different version of it - i.e. it has been erratad since its original release - you'll have to reach an agreement on that Power with the DM and the other player. You either may use a different version or, more probably, agree to use the original version for this power.
It all depends on how eagerly you want to join this group, but it's definitely your task to adapt to their style.