I think Specialized put components on the bike where it mattered, with the exception of the xtr rear. xtr rear was purely for marketing purposes. Doubt there is any functional difference between lx shifters & xtr shifters except weight & finish quality. Personally I also think that the Deore cassette is the same as the others too, except for weight due to steel vs alu parts.

My 06 shifts fine in the rear in all instances. The front fine except under load, where nothing will shift properly anyway.