That's a good point. Not to beat a dead horse, but there's also the part where Dr Roberts tests differ wildly from Lucky Gunner's, and that 357 provides negligible difference in snubs to begin with.
About the only 357 I'd put through a snub is the new-ish Gold Dot Short Barrel, and even then its more of a +p than a real magnum. Given they already make a 38+p Gold Dot SB, I'd guess that Speer would have made the 357 SB version as Magnum-ish as possible, and that its current specs/performance is reflective of how much Speer could squeeze out of a snubnosed Magnum.