Well I guess I've started interesting discussion, even if it was under a rather Anglocentric misapprehension!
I think we can confidently say that this discussion proves the value of forums. One starts a thread with a notion in one's own mind, and lo and behold you get loads of helpful responses proving the exact opposite! Certainly I had the diametrically opposite notion to you in that I always considered roundhouses in Britain a total rarity, having spent much of my youth observing European roundhouses!
There were some incredibly impressive roundhouse complexes in France, for example at Nevers,
In this blog I found in a search there is an aerial picture showing the surviving complete roundhouse and to the right the evidence of the second one (which I recall as being open to the air)
http://veaugues.over-blog.com/article-visite-au-technicentre-sncf-de-nevers-123505090.html
and going back to the subject of Germany being 'too modernised' for roundhouses - what actually happened there is that roundhouses were kept and modern facilities installed such as the complex 'spiders web' of overhead wires needed to make a roundhouse suitable for electric locos.
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