Well, how about inserting such language in the body of the claim in the first place? Is it really that hard? If you insert the preamble language into the body of the claim in the first place, examiners have to consider it as a claim limitation, period. Why not prevent the problem from happening in the first place?
Simple. At the time of filing, we might not know whether the preamble language is needed to circumvent art later cited by the examiner. However, the law is quite clear that we are allowed to make preamble language limiting by merely saying so. This is the law of US patents and the examiners are charged with examining US patent applications in the context of this law. Whether they like it or not, that's the way it is.
Seems slightly inconsistent, though. If you're not sure if you want to narrow the claim down to the preamble language, it isn't too unreasonable for the examiner to look for art that falls outside the preamble.
I also find myself agreeing with Robert FWIW.