I Personally find the price range is a major factor for me, buying a unit of troops for Tyranids is murder to get a full squad and after trying to play Tyranids in 40k and watching most games devolve to whoever takes most tanks wins (gaurd) in the recent editions of warhammer I decided i liked warmachine better and find the play system far more enjoyable although i still intend to work on my 'nids' I'm waiting for the 6th ed to come out