Of course, it's easy to point out that Accucraft UK tends to go for smaller engines than their American counterparts, it's also important to remember that while something the size of a USRA Pacific (or a Southern Pacific P-8, coming eventually to an Accucraft dealer near you) would be considered relatively small compared to all the 4-8-4s and articulateds, it would be considered a BIG engine for much of Accucraft UK's market. By UK standards, the A1, A4, and Merchant Navy are all very large engines.
One thing I have noticed though, is that the UK models seem to follow a philosophy of producing beautiful, well-detailed models that are ruggedly simple in the mechanical department. While we over here are demanding things like cross-ported D valves, fully functioning valve gear, axle pumps, metering lubricators, etc. etc., over there they are merrily producing two-cylinder models of three-cylinder Pacifics with slip-eccentrics, that by all accounts run very well. My GWR 2-6-2T, beautiful engine, love it to bits, but no frills under the hood (er, bonnet); unsprung drivers, Ruby-style piston-valve reversing. And that's great, it keeps the cost down while allowing them to produce attractive, moderately-sized locomotives that run well and apparently sell well too. Of course it also helps that the generally clean lines of British locomotives mean that fewer bells and whistles (quite literally in the case of the bells) are needed to make a "well-detailed" model too.
Would that kind of philosophy work in the US market? Hard to say, the 1:29 stuff seemed to go that route, smaller prototypes (4-6-2, 0-6-0, 0-4-0), simpler mechanics, lower price point, and that seems to have been maybe not quite the success they were hoping for. I suspect, however that it might say more about the 1:29 market than it does about the AML locomotive design and pricing strategy. 1:29 as a scale seems to be more geared towards modern era modelers and those who just like to run toy trains, who simply don't have either the interest or the budget to splurge on a live steamer, even a well-detailed one that squeaks in under four digits (barely).