chrisstep,
I think it would be fair to say that most of us here on expat contracts, would not be here if the allowances were not included. You may be here for the food, but I know I'm not.
Your likeness of the local chap going to BA is not a decent comparison. The skills expats offer are in demand in HK, thus they have to pay a premium. Do you think CX or KA would pay housing allowance to expats if they could employ locals to do the job!
Think about it.