As far as I've seen it's a matter of what they think the players want rather than any legal fears. They have said that unbranded content doesn't sell as well (and more difficult to develop without inside help from the licencer) so they tend to avoid it. Cheers
It's funny that they don't do unbranded trains but are okay with running completely inappropriate trains on routes.
Doesn't change the fact DTG have used such logic in the past to justify their decision. Simple fact is that logic just doesn't make sense as long as third parties make unbranded content. Besides, the logic you're using would apply to third parties, but evidently they still see demand for such content regardless. Not impossible though, and often they do develop content without access to locos and the route in question. I would also note depending on the route they wouldn't need access to locos, because they could modify existing stock. For example I see people bring up the Metra Racetrack as a route that would work well for TSW. And in terms of rolling stock you could get by with a similar lineup to Peninsula Corridor. In fact I think the only loco the TSC version does have the PC doesn't is a P42, and that's AI only anyways, so playable content's pretty much the same. Also what exactly stops DTG from working with some of their existing partners or contacting other parties to get the info they need? Very few railroads use truly unique stock that only exists on their line these days. You could source info from other partners to help fill in the gaps. SCS did that with the Cascadia for example, they couldn't record sounds with Daimler, So they got in contact with a company in Europe that was able to do so.
But most railroads will have their own slightly different spec and the forums would be awash of nicpickers pointing out that x train company uses Philip screw heads and the model depicted has flat heads.
