Time
&
Time = Money
Mods take time to create. Mods take time to optimize this time must be spent by someone. Modders spend their time for free and doing such while Bethesda Game Studios and all 100 (or is 99 now) developers is on a Job working being paid for their work.
Any content released by BGS via DLC is just a mod period an official mod but still is a mod to the base game. The content that you will get from BGS will be optimized (or at least more so to an extent of some user made mods created by 1 person vs 100 can do) and able to work on each platform.
Taking the "best" or "recommend" PC mods will not exactly do so well with console for one high res textures cannot be done and two things like SkyUI is PC focused not meant to work with a controller still does though.
As for the game editor idea, this isn't Halo this isn't a small ass FPS "HALO paced" map this is Skyrim one of the LARGEST worlds on consoles (beaten by Just cause2, farcry2 come to mind) it has separate cells tons of separate cells even releasing a console to the consoles could result into major issues of the user overloading their systems even to the point of frying the system because heat control isn't all great especially if you never replaced the heat paste. Let's imagine that this was possible/permitted and In this scenario where a user of the 360 spawned 10k cheese wheels and broke their game or even console who would be to blame? MS they will laugh in your face after going "Well BUY another YAY" sony will have the same. Bethesda would most likely put up warning for mods and say "can't help ya".
So yes DLC whatever Bethesda's releases later this year for the xbox getting 30 day head start is logical it is fair because the mods on PC someone has to create them spend their personal time doing such for free going through several versions and testing to get it working for a good amount of people. That's what is good about any modding community for any game people spend their time doing such for others improving the game play of said game I did the same in Crysis/wars people did same in Battlefield 1942 through 2142 and people have been doing it in TES for the longest time as well as many other franchises.