LEVICOLEMAGIC,
They differ just for the sake of being different and also because they are just plain cruel. They love to punish the flock and deprive them of simple pleasures. There must have been some very masochistic, miserable, sour personalities in this religion and somebody decided 'no holidays'.
Of course, their reasoning is pure crap. How could anybody think there is something wrong to get together and spread out a nice meal for relatives and some friends? This is particularly painful for singles in the congregation and bothered me, particularly. Why would Jehovah only be pleased if I am home alone staring at four walls? Does this make any sense?
I also suspect they disapprove of JWs getting together with non-JW relatives because they are simply afraid that the JW will get unconditional love from their non-JW family and will REGRET they ever got involved with this vacuum of a religion.