My last car that did that had a dead shock - but if it is identical on both sides, I'd imagine it is more likely to be a major alignment / bush problem. Is the Mk5 independent rear susp? or on a trailing beam?
If it is independent, it would be bizarre that both rears could have uneven inner tyre wear - as this is a sure sign of a fault on both sides. If it is a trailing arm assembly, some play in the bush that holds this could cause that problem (I forget its name, the mk4 had one)
I would really press VW, because aside from an unsafe car, you have 2 prematurely dead and expensive tyres.