Hey There,

I have google alert me when the words screwcap and oxygen get published together.  I am the inventor of the newer oxygen-regulating screwcaps (Smartcaps) and run a company which produces the same.

There is an alternate explanation that has not made it into public knowledge that really should be:  There is an unacceptable amount of variance in the quality of the surface finish for the glass bottle out there - from particular producers.

This roughness is a result of the glass molds not being cleaned out often enough.  Although screwcaps are typically very high barriers to oxygen, all of that goes out the window when the glass is not up to snuff.  The bottles in question would also quite possibly leak if they were turned on their side.

So it is quite possible that someone might be seeing a high incidence of oxidized wines if they are buying from wineries who use one of these lower-quality bottles.