Dig, back to the original question for a minute, it is difficult to compare the UK with the US per se. Really what you must do is compare the UK with each state in the US because each has its own traditions and hunter visibility requirements. Indeed, in some states those requirements vary depending upon whether one is talking about private or public land. I have had the opportunity to hunt both in Germany (a lot) and the UK (a little) and in both settings the traditions, limited access to hunting areas, and the highly controled methods of the hunt itself make high visibility clothing of limited value. The situation is quite different and varried here.
I suppose, we really have two broad movements in this country that have affected current "rules" on attire. Depending upon which a state has embraced, it has driven the amount of regulation imposed upon the hunter. With regard to big game, I suppose Texas would represent one extreme, and perhaps Pennsylvania another. Texas has a tradition of private land ownership and "ownership" of the game on that property. There is very little public land available and the lease system, owned by individuals, clubs (syndicates in British parlance), or commercial hunting companies prevails. The seasons are fairly long, the selectivity of the harvest is generally quite high, and as a result the "nanny" factor is quite low in Texas, and there are essentially no hunter orange requirements. Pennsylvania, on the other hand, has worked hard to provide lots of public land with lots of deer, for lots of hunters, taking a huge harvest, and with very little time to complete it. As a result, the management/oversight factor is very high and hunter orange is a prescribed uniform.
Hunter orange is a somewhat different issue for small game, and again varies from state to state. My unoficial survey would say that most of it is worn voluntarily. Most of this shooting is "rough shooting" on ground that is often very rough indeed. I often hunt quail and pheasant with friends who are as experienced bird hunters as one could ever hope to join up with at the south end of a pointer. In Kansas and Oklahoma we are not required to wear hunter orange but we do; not because anyone is remotely unsafe, but because flushing birds and high, thick brush would give even Lord Rippon a bad day (ask our Vice President).
With the disclaimer that no generality is true about a country as large and historically diverse as the US, our dual traditions have also driven the development of hunting clothing. Prior to the depression hunting clothing trended toward what we now think of as traditional canvas shooting jackets, lace boots, and weather dependent hats. If you look at the old photos, it is remarkable how many nimrods, even among what we would now call the middle class, were wearing ties as they uncased their L.C. Smiths and Parkers. At the same time a larger group of Americans were hunting in whatever servicable clothing they had for both recreation and subsistance. These were the largely rural families who made up most of our poulation until WW II. That subsistance notion gained traction with the coming of the depression. Game management came to reflect the blending of those cultures and clothing has followed suit. Perhaps one end of the spectrum today being the cammo clad deer slayer using his plastic stocked .300 WSM on the Saturday morning sports show and a member of this board wearing Filson taking his SXS into a grouse covert.
That said, I, like many of the writers here, embrace either depending upon the season, the game, and the regulations of the jurisdiction in which I am hunting. In short, there are few simple comparrisons with the European hunting environment. All that's good, Joe
