My understanding is that it is more about consistency (and in this case left over sugars). If you bottle a barleywine after 1 month, and then age for a year, the yeast all change the beer in slightly different ways. If you bulk age, all of the beer ages the same way.
I'm happy to be corrected, but I'm not sure I buy that theory. A properly mixed beer with priming solution should be homogenous from racking into the bottling bucket, so there should not be inconsistencies like that. Yes I can understand bulk aging to be sure you don't bottle too early and avoid bottle bombs from tired yeast, but I don't buy the argument that they'll all have different sugar amounts in there if you don't. To me that just suggests poor bottling practice.
I'm not sure that it's necessarily poor bottling practice as much as it is the increased number of variables that you have from bottle to bottle. Bottle size, shape, fill level, amount of oxidation, priming sugar, etc. I doubt that anyone on a homebrew level gets the exact same amount of priming sugar into each bottle.
I'm more familiar with long-term aging of wines than beer, and with wine you can get significant differences between bottles of the same age. Also, magnums age differently than 750ml bottles, so volume may have more of an impact than you might think. Temperature has an impact on aging and a larger volume should maintain a more consistent temperature with respect to variations in ambient temp.
Currently, I bulk age all my beers since they are in kegs. When I first started brewing higher gravity beers, I would leave them in the carboy for months but found that to be a PITA after awhile (after 6 months or so, I typically needed the carboy for another brew). I've found that I have the ability to keep bottled beer much longer than kegged beer since I can stash bottles and forget about them.
On a commercial level (although I'm not sure who does significant aging on a commercial level) I do believe that bulk aging would be used for consistency purposes, particularly to eliminate any variables in bottle storage, etc. prior to release.
Like a lot of other things, I would be that on the homebrew scale the impact/difference is minimal.