Indeed 
I believe some american made 7x57s can have shorter throats, perhaps upon request. But these were made before the modern (ever stronger) growing push towards non lead, so they might go back to the longer throats in the future, i suppose.
But as i read the america gun writer, who himself uses the x57 quite a bit, it isnt so much short vs long throats that's the problem, is that there can be found a good bit of variance even between longer throated rifles.
But as Heym said, if you're tailor making your loads anyways in the right way, it probably holds little importance. If you want a cartridge where the chance of using someones elses load recipe with quicker and more frequent success , a cartridge with less variance on this area is perhaps better.
But again i dont hold vast relaoding experience, in fact i am only getting started. This is just what i picked up when ressearching reloading the 7x57, prior to that.
EDIT:
John Barsness is the name of the 7x57 using gunwriter i have mentioned in this thread. He posts as Muledeer over on 24hrcampfie , i believe, and has written several articles and posts on the old 7, and on reloading for it, including the throat factor.
Nathan Foster on his 7x57 page, also mentions the variating throat lengths that one can experience with 7x57s, and the effect it can have on muzzle velocities.
