Steam pre-reg codes not cross-compatable with Windows version registration

[SecretCrowds]

To give some examples, I bought Rift on PC, and can play it on Steam by simply downloading it. I can then play on or off Steam without any issues.

That is inaccurate. When Rift was P2P, you had to buy the steam version to play on steam. And all steam versions were locked to steam only, having their own expansion too (even their own bonus).

You can link your launcher to Steam but it wouldn't have any of the features you would have if you bought Rift from Steam.

Of course, now it's different since Rift is F2P but you definitely needed to buy Rift on Steam back when it was P2P. However, if you play Rift through Steam now, you can't buy credits using a Trion account but only through Steam Wallet. Steam definitely imposes restrictions on non-steam versions.

Steam vs non-steam PC has even more restriction than PC vs Console.