If I remember, there were three trains built. All were given a 4-4-0 wheel arrangement if my mind is together as I type now, which as one could imagine greatly cuts down on costs for design and construction as parts can be cast/produced in bulk to similar patterns. While my guess is they're pretty much mechanically-identical (think DLRR 1-2), I'd bank that what the locomotives lack in a boiler is made up for by cosmetic detail and appearance. They're probably full of cosmetic character; each with a different theme and personality. Sort of like Fry's Electronics stores!
It also as-stated must be kept in mind the Imagineers themselves are working under hard circumstances due to the company's executive division as well. I'd certainly think probably some of the guys responsible for those trains are steam fans themselves; and probably had the bite the bullet in going for diesel, probably at corporate's orders. I once heard the reason for no steam was "pollution standards". I find this hard to believe; especially since the propane firing option puts out as much emissions as the gas range in your kitchen, but whatever. The order for those trains was placed quite some time ago; which shows it was obviously taken care of early for its known importance.
Kyosan Kogyo of Japan, and the Tangshan Locomotive Works in China both continue to advertise and/or manufacture steam locomotives. China is starting to electrify, slowly. Hong Kong is a modern city by all means, regarded by some as comparable to the New York of China. As Michael stated in unpredictability...why is Casey Junior the way it is? (obviously, they had enough trouble getting it done on internal combustion power as it is). Some railroad is better than nothing at all. If a certain management is unable or unwilling to properly maintain a steam railroad, it's also probably better it goes its own way as well. The real problem I'd have would be 'lowering standards', such as conversion to diesel years after a locomotive has been constructed and operating under steam. Six Flags over Georgia comes to mind. As long as the Disney steam railroads we've got remain powered by live steam, that's good enough. I never really planned on passing through Hong Kong anyhow, so it doesn't affect me. Yes, a steam railroad would be better...but as long as what we have stays, it's good enough.
Steam outline locomotives have their place; I never imagined it would be on any Disneyland Railroad. A few years ago, the Billy Jones Wildcat Railroad was seeking a 2nd diesel locomotive (since the line's only other motive power, steam locomotive #2, was down...and the other steam locomotive a mere pile of parts with no suitable boiler). I was working in the enginehouse and found a stack of papers on Chance Rides C.P. Huntington trains, and knew what someone was thinking, and made a nervous laugh. The board of directors did the same, stating the railroad's essential "make it look like what it is" policy. 2-spot looks like a steam locomotive, and is; 2502 looks like a diesel locomotive and is. While I hate to say it, amusement park steam operations aren't tourist railroads; to the majority of the visitors, and sadly to management in some cases, it can be "just another ride". I personally would rather see, if a steam railway was ruled 'not an option', that a park's diesel locomotives looked like what they are. Yet again, the public wants a steam locomotive, and as proven on various threads here and elsewhere, sadly most of them are unable to see past only looks. That's just how it is. The majority of the people in my current area I guarantee have never seen a steam locomotive in operation, with the exception of the WDWRR...maybe Busch Gardens' Crowns. The thought of a steam locomotive being treated as "Just another ride" by management is truly a scary thought. The crews for the most part know what they're doing; any trouble usually comes from corporate preventing them from doing their job. Lucky for them, they have the option of not having to put up with it.