Originally posted by m42man
If the focusing mechanism causes the lens to "telescope", then it means that air (and that might be humid air), water or fine dust may be drawn into the lens during focusing - I can't imagine such a lens being designed to allow internal air pressure to be substantially different from ambient atmospheric pressure (but I might be wrong). Hence the "normal" lenses have to make do with "WR", which probably just means that air is allowed to flow into and out of the lens in a manner which is more controlled than is usually the case.
M42man, you are overlooking the fact that the DA* 16-50 telescopes as opposed to being an internal zoom like the 50-135, and yet they both have the fully sealed designation, unlike the WR designation, which has been used for both telescoping lenses (18-55, 50-200, 18-135) as well as a prime (100 macro). So I don't think whether the lens telescopes or not is where the difference in how weather resistant they can make it lies.
I asked Ned on his blog and all he had to say was "if it is drizzling outside but you can still wear a sweater, that is WR weather, but if it is pouring and you need a raincoat, that is DA* weather. He said bring a towel to wipe down either in wet conditions. In conclusion it seems there will be no concrete answer as to WHAT the difference is, but unless the whole difference is a hoax by Pentax to promote their top of the lines series, which I greatly doubt, we can conclude the DA* designation means better sealing/proofing than the WR designation, something that many people are unaware of I found as I did my research, as many old thread have people referring to DA* series lenses as being WR. I guess Pentax will only go as far as "sealed" and "simplified", and if you want sealing that is up to the level of a K-7 or K-5 then the DA* are the answer. Ok Pentax: change the SDM motors to something reliable and I'm in.