Probably a difference in ingredients, I doubt any of the breweries are using sulphites, anything over 10ppm requires a warning on the label (as with wines). The "sulphite headache" from wines is actually attributed to Histamines which are produced during the malolactic fermentation of red wines. White wines generally have a higher level of molecular SO2 than reds due to their increased susceptibility to oxidation.
I would look to ingredient differences for beers.
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Bourbon Barrel Imperial Stout
On Deck: German Lager