Good Morning All
Yes, the Steam editions of Trainz Simulator 12 do have a full Trainz Simulator 12 serial number/cd key. However, this is only accessible once it has been installed. The 'steam key' that is supplied in the 'bundle' is the key needed to activate the software on Steam, and this is outlined in the system requirements (and shown by the multiple times it mentions Steam for the software).
@RRSignal
If you do not wish to use Steam, then this is your choice. Despite what you may feel about Steam, this is a fully copy of Trainz being sold in the bundle and is not 'junk'. It may not suit your own purpose, but that doesn't mean it's not suitable for other people, and calling it 'junk' is not appropriate (unless this is your feeling about TS12 in general, then that is fair enough).
Again, as above, once installed, you receive a cd key/serial number. Which you will then need to use to register Trainz in your account. Steam Keys and the Serial Number/CD Key are separate parts of the Steam system. One is used to activate Trainz in Steam, the other is used to register it in your account. In theory, the serial number/cd key could would in a non Steam install, but I have not tried it, so cannot guarantee it (I know the earlier DLC packs did work in non steam installs though).
I would ask you to correct your signature to reflect this correctly. As a note, the TS12 from Steam is basically the same as TS12 SP1 HF4. There have been alterations for Steam, however these differences do not change the functionality of Trainz itself.
Regards