I wouldn't think the expansion/contraction issue would affect anything structurally, since we don't feel any resistance when zooming. If it were building that much, the lens would tend to suck back together and get shorter as we zoomed it longer. So that leads me to believe that the pressure/vacuum created would be being released somehow. I think this is the point of contention - HOW is it released, and if so, does that lead to a point where dirt/moisture can get in? I would hope, since these are
designed to be water resistant lenses, that a method has been
designed in that would filter the dust/moisture at a controlled location so it doesn't cause problems.
Is anyone willing to tear apart their * lens in the name of curiosity?
I'm sure that there aren't
that many parts...