It doesn't really provide an inferior service, but Bethesda games (Fallout, Oblivion) have been known to have Mod issues with the D2D version of the games, something to do with the script extender not working with them, which would preclude people from a lot of the great mods coming for Skyrim, that's the only possible issue i can see with the D2D version.
As for which version begins downloading first, it's a rather Juvenile and irrelevant argument, as both will most likely be ready for launch regardless.
Neither of those titles are steamworks. the reason there is an issue is because the native d2d executable for their games is encrypted, which causes problems with mods.
that wont be an issue here, because there is no "d2d version" perse, they are reselling a key for a steamworks product. weather its steam, store bought, d2d, or any other retailer, the installed game will appear and function the exact same.