I think, it's just ploticis. The only reason for non-implenting the freetrack thing is maybe a deal with the guys from Track IR. The exclusive rights for supporting this game with Track IR.
And if somebody would ask me:
What's the difference between using Track IR or Freetrack?
Track IR comes for about 160Euros
FREETRACK comes for 45Euros (with Wii mode and some IR-LEDs)
Arma2 is the best game I ever played. I would be very disappointed if BI would lock the Freetrack users out.