My 2 cents worth, lets think about something for a minute. Grand Theft Auto (GTA) has a budget that suits the game as the designers know that they are going to get their money's worth and then some soon after its released because they have targeted the game to a wider audience that is into that sort of thing. (Smashing up cars, killing peds, following a story line, etc.) By an audience is constantly buying this sort of game, the developers will invest in this sort of game as it makes a lot of money. (Modern games also have several hundred or even thousands of people working on a title - from coding to artwork.)
Now, Trainz is a niche product - as in it appeals to a much more narrower audience than shoot 'em ups lets say, if you did some serious market research, you'd find the sales of Trainz to be quite low in comparison with GTA (in fact a flop in the ocean, probably less than 1/100th - someone needs to verify that first), which means the budget is going to be far less than that of GTA. As a result, you have fewer people, which in turn, means longer timeframes or even eeking out as much life from the product as possible.
However, involving a community is probably one great unique thing about Trainz, which has one big problem that has yet to be addressed when creating assets. This is also a problem that haunts a lot of open source software and a lot of addons.
Standardisation.
Why? Play GTA for an hour and you hardly notice the difference between each assets, even if one person was allocated a car to model throughout the year each and one person produces the coding, therefore everything fits in. Play Trainz and you will soon notice who created what, because the "standardisation" isn't either there in as much detail or creators choose to ignore it (myself included.). This can be because of several factors. Skills, timeframe, etc. The answer is to have a set of common goals which are rigorously enforced (Railworks anyone?) and content creator guides that are far more indepth than we have of current, but this increases development time and you need someone to enforce it if the resources are there.
That is probably why you will find a consistent look across Raiworks, but not Trainz. (However, Trainz does have 13 years of development, whereas Railworks only has 6 - if that.) Apart from that, comparing to the other sim unfairly (Sorry!
), there seems to be much better "shaders" (bits of graphics code, if you like) available at my disposal and more standard maps at my disposal than in Trainz, for example the environment mapping which is the gloss like effect you see is the same for all stock. The lighting is the same for all stock. Etc, etc. Then you run into a challenge in how to keep all the assets "consistent" between creators.
It has been done, look at some add-ons produced, like Skipton to Carlisle. That has a more consistent feel than Trainz itself but it was a community lead project.
