..well, seeing as you have a ticket hoisted on these things,
which likely will only be answered by the 'try it and see'
route, I'll leave most of these questions to be replied by
whomsoever fields the ticket...
My ticket got a quick response --- excerpt --
"The short answer is that DDO and LOTRO via Steam do not work in Crossover. "
To make a long story short, my original analysis is correct -- The Turbine Launcher does not work under CO on the Mac, therefore neither does the Steam version of those games.
...what I did want to affirm, here, is that Steam is very
unlike PMB.exe in about everyway possible I can immediately
think of (in comparison)...
There is Steam, and then there is Steam. "Steam," as a platform, is like an X-box, Atari, or PlayStation. It's an environment which forces you to do things their way. It happens to be a large environment, but there is no compatibility between say, a person playing standalone DDO and Steam-DDO with respect to voice chat. Each environment has its own system, and the two are not "cross-compatible."
From everything I understand about Stream and Pando -- Yes, the two are virtually identical as digital distribution schemes. Both charge the original developer of the game a Fee to re-distribute the game. Other marketing aspects of the deals are just that -- contractual items between Valve and the original developer. Valve/Steam offers a developer many features beyond their own game, but they are exactly that -- features beyond the scope of the original game.
As for specific differences, Pando (PMB) uses a Torrent style downloader -- Steam, apparently does not.
At least at this time, WB/Turbine does NOT use any of SteamWorks features. That might change in the future, but current statements from Turbine have said they (via the Turbine Launcher) will continue to handle all authentication/updating things themselves.