Both. The deveoper's excuse was that it wouldn't fit on to the CD. Maybe if they hadn't dedicated so much of it to all those proffesional 'mods' then they would've had the space to add in the Editor. They expect you to use your own graphics program or the Editor that shipped with FW/MGE.
There is a conflict between the 'Units' files of the two versions because ToT uses additional unit slots that aren't used/exist in the FW/MGE file.
In other words, you can use the FW/MGE Editor for everything in ToT except the 'Units' file.
What you can't do is import an image file from ToT to FW/MGE using the Editor --you get the "Image is not 640x480x256 color" and "Invalid File Format" popups.
(For anyone reading this, correct me if I've missed something.)
It's really too bad that ToT has these limitations because the addtions to the Rules.txt file are very helpful (i.e. Impassable Terrain, 'Invisible' unit flag, 'Unbribable' unit feature, more unit slots, more tech slots, additions to 'Comic Principles,' ect.) and some other features like the one that flips the unit image (horizontally) when the unit moves West definitely makes the game look better --not to mention the multiple map feature. Frankly, all this should have been in MGE.