Train Simulator should both be on and off the list... here is why:
If you bought it back in 2011 you automatically get updated to the latest version, also every version comes with unique tracks/trains and other goodies to validate the purchase, at a cheaper price than buying em individually. so think of it as "Starter pack" instead of buying "the game".
In fact some people buy the new "Starter packs" even when their base games got updated to the latest for free, in order to get the added content for a much lower price than buying them as DLC's
Also its one game where you do not need to buy all the packs at all, in fact if you do that you doing it wrong. Think of Train Simulator in the same light as people who have actual train sets, its for enthusiasts not "gamers"
Edit: Oh and I forgot most of the DLC, Tracks and Trains start their life as community workshop content and some are so good the developer "port" and "combine" them and make actual pay-for DLC where the original creators also get financially rewarded. So if you dig long and hard enough you can get all the content without paying for it.