heres the thing, SC2 edting differs from warcraft in a few ways:
Warcraft 3:
-creeps, starcraft 2 for all i know doesn't have them.
-Heros, they lvl up and make great RPG games, + you can make wow instances.
-Spells, warcraft 3 has lots and lots and lots of spells, SC2 doesn't have things like wardens fan of knives.
-Items, SC2 may not have items or attributes for heros.
SC2 modding:
-starcraft maps, like TD or someone may make a Zergling extermination game.
-people may just make big battle maps, like you control a special ops unit, you control him and only him in a huge battle around you.
WC3 and SC2 will not cancel one or the other out, SC2 might be easier to use but warcraft three has many things over SC2.