For many people the answer to this question is simple, because we tend to think in categories of theme park games versus sandbox games. SWTOR like WoW is definitively theme park, Skyrim is far more sandbox. But having played a lot of Skyrim between the SWTOR beta weekend and the early access, I couldn't help but notice that the reasons why I play Skyrim and not WoW are very similar to the reasons why I play SWTOR and not WoW: SWTOR and Skyrim are full of interesting stories, while WoW is more about execution and gimmicks. SWTOR and Skyrim have worlds that are coherent within themselves, WoW is far more of a mishmash spanning everything from jokes about goblin bling to dramatic high fantasy and science fiction in a single game. In short: In SWTOR and Skyrim I care about what happens, the characters, their motives, even my dialogue responses that aren't linked to any point gains. In WoW I just click accept without even reading the quests any more, and I visit dungeons without caring a bit about why these bosses are in there waiting for me.
Now part of this is certainly an effect of simply being new. I fear it is inevitable that sooner rather than later the theorycrafters will try to ruin SWTOR and tell everybody what morons they are if they aren't using the optimized talent builds they developed. The day you chose "boring talent A" over "fun talent B", just because talent A gives 1.7% more damage per second than B, is the day you effectively decided you care more about the game than about the world. At some point the decision of whether to go light side or dark side in SWTOR for some people will be made based on arguments like "but light side gives better gear for jedi knights". And then the lore and the stories stop mattering and we are back to World of Warcraft.
How fast and far this will develop probably depends very much on how difficult endgame "raid" instances in SWTOR will be. I get tons of negative comments every time I ask for MMORPGs to have relatively easy endgame raids, along the lines of "u r just too stupid to play hard raids". But fact is that the harder you make content to beat, the less options players have to beat that content. If players really *need* the 1.7% more dps from talent A to beat the typical raid boss, it is hard to blame them for all using the same cookie cutter build of the month. If the challenge is somewhat easier, different combinations of talents and tactics can all work, and we end up with a more interesting and varied MMOPRG because of that. One that allows us to still care about the world and our characters, and not only about our stats and performance.
Even if Star Wars: The Old Republic isn't exactly a sandbox game, I would certainly call it a "world" MMORPG, as opposed to the "game" MMORPGs like World of Warcraft. At least for the moment. We will see how this works out in the long term.