I think I would debate this point. In higher end brake housing or spiral wound housing for shifters, they do try to wind the spiral very tightly to minimize compression. But I have seen lots of brake housing that clearly compresses under the pressure of braking. This gives cheaper cables that 'mushy' feel and will mess up index shifting when brake housing is used by mistake. I've caught this on several bikes as the problem when shifting will work fine at one end of the range, but gets increasingly bad as there is more tension put on the shifter cable. I assume you were referring to spiral wound housing specifically for shifters and in that case you're probably right that the changes in the cable path are the critical issue. But just to be nit picky...