Notice that the English guns that were mentioned by Roy are, for the most part, guns designed to handle heavier loads. There is a good reason for this, not lost on the British. Heavy recoil is much harder to handle with a straight grip. Those who espouse straight grips for all S X S guns are ignorant of this fact. Ignorance is simply lack of knowledge. Anyone who has tried using heavy pigeon or duck/goose loads in a straight gripped gun soon learns that it is impossible for the average man to recover from the recoil of the first shot and get the second barrel on target as well as he should be able to. Pistol grips allow much more control during recoil, and the second shot is able to be brought to bear with much less effort. Nash B., as we know, had Bo Whoop built with a straight grip, but he was a big man with big, strong hands. Look at photos of him in his prime and this is easy to see. I can tell a huge difference when shooting my straight gripped A grade 32" Fox. I'm not a big man, nor do I have exceptionally strong hands, but I'm no wimp, either. I tried shooting a 200 bird state championship sporting tournament once with that Fox. Never again!
As additional proof, consider how many heavy recoiling double rifles you have ever seen built with straight grips. There may be a few around, but I've never seen one. And wouldn't buy one if I did.
SRH