I agree with Antoni. Siberia IS synonymous with severity, and the when the word "Siberia" is spoken or written, the correct picture is immediately seen in the mind the world over. When speaking or writing about the subject, one can state: "...to Siberia and other areas of the vast USSR." To split hairs over the place of incarceration detracts from the cause as a whole when giving a speech to school children, for example. On the other hand, there were some that were sent to (technically) Siberia anyway, so this point is, in my opinion, moot.
In my mothers view, who was there, Siberia was a geograpahical area, and not as you suggest, 'synonymous with severity'. I think that historically we need to become more factual rather than expressing view points which may have nothing to do with fact. Basia