if you perk farm in EW/MW to use them in LW ... you have no style.
 
  It is an option?  And here, all this time, I was having too much fun doing this in LW. 

  Oh wait... 

I tried this once...found it BORING as hell. 

  It's more fun when there is a chance to be intercepted or even shot down vs farming in the other arena's were your BIGGEST threat is a disco.  I get plenty of perks for shooting down planes AND blowing stuff up, even if I don't make it home. 

As for the OP, it would not bother me one bit if the perks were separated between each arena, however, some folks who play LW for a while may wish to go into the other arena's for kicks or to plain get away from the LWA.  Having them start from scratch would make it a little frustrating for a few of them.  The numbers are quite low in EW/MW compared to LW, meaning it will be harder for them to find enough fights within a reasonable amount of time to rebuild.  MOST of the time I log in, I see EW sitting at 0-5 and MW 0-10.  Honestly, if I wanted to go there, but had to start with zero perks, I wouldn't bother.  I am guessing that HiTech has it the way it is because it's easier to keep perks and let them be used in the other 2 arena's vs losing a customer entirely because they have to rebuild their perks from zero in arena's that are ghost towns.