busy creating snow cat simulators
Remember, we are also publishers (note, take a look through the N3V Games store, there are many games in there, the majority of which were developed/produced by other companies). In the case of the new 'simulator' series, these are mostly created by a company called UIG Entertainment, and not by us. We simply sell them through our store. Some of them have sold quite well too
As for frame rate munching, I get good frame rates on my PC (Core2Quad 2.8GHz, 4GB RAM, GTX260 1792MB, Win 7 Ult 64bit). Granted, not everyone has a higher end machine, but then it should be expected that newer games do require newer spec computers (imagine if the latest Need For Speed games needed to run on machines that NFS Hot Pursuit 2 ran on... - note this version chosen since it does date from a similar time period as the original Trainz releases for a similar development period).
You'll find that a big part of frame rate
is that we have to support 3rd party content (20k poly cars, with 15 odd textures, and no LOD anyone?). Granted, the built-in content tends to avoid this (so as to not require $10k computers to run it...). Also remember, the minimum spec is the
minimum required. You'll likely need to turn the detail settings down (I still can't run a fair few of the FPS games, which tend to have very short draw distances, at max detail).
As for DLS content. As has been said, if we implemented a minimum standard, you might find a lot of content doesn't go through (seeing as what might be my minimum standard, is much higher than your minimum standard, and might be higher than what some people may be capable of doing when starting out).
Granted, some 'rubbish' (again, what I consider rubbish will be different to what others think of as rubbish, aka one mans trash is another's treasure!) does get through. But, if someone can find a use for it, then (personally) it was worth it. Even if it is for an 'easter egg' on their layout

You never know, you may just download a layout that uses one of this person's ground textures to an interesting effect (much like I've seen maps with a ground texture that has big red writing on it saying "EMPTY SPACE" in some spots). And then you might just be glad it got left there...
A good example is Paintshed reskins. Sure, they may not be your cup of tea, but if someone gets enjoyment out of a creation, then it's generally worth it.