Good afternoon Tom (at least its afternoon where I am at the time I'm typing this
I hate to say it, but I have such a bad attitude lately towards JW teachings that the first thing that popped into my head was "they can do it because they say so".
If you look at any of their beliefs, it all boils down to that statement. Its this way because they say so, doesn't matter if it doesn't make any logical sense, doesn't matter if it can be proved wrong. Its the truth, oh yeah, except until they change their mind, then its "New truth" or if its old enough they will say that they've always taught that, even if you can find in their old writings that they didn't.
Again, sorry about my attitude, my bad.