I'm not necessarily the biggest MMO fan or player, but from what I've seen, all a company needs to make a profit off of a MMO is a relatively wide fanbase (who may need a little refresher on the main topic) and a pretty easy, basic story and game mechanics. After that, the MASSIVELY part of the MMO genre should kick in, because there needs to be an expansive universe for the player to make their own decisions and craft their own 'life'.
That's what made WoW the phenomenon it is today; people who loved playing Warcraft and Starcraft jumped at the opportunity to get in on Blizzard's newest endeavor, and combined with an easy to learn, yet expansive world, the ball got rolling and never looked back. On a side note, how cool would a Starcraft MMO be? But I digress...
What made Galaxies so great is that it tied into the movies pretty well. People who don't delve into comics or books or anything else StarWars except the movies still could go around and have a good time, because they still could figure out what's going on.
Here, with SW:OR, there's not really as big an interest, or a knowledge base. Unless a person has played KoToR (2), or delved pretty extensively into the literature pertaining to it, there's not really a whole lot of common knowledge about this era in StarWars history.
As far as the whole technology/aesthetics/"different eras but they look similar" argument...well, there's no real, easy, logical answer. As far as a corporate standpoint goes, it would be smart to give people something they recognize, because, as my above point stated, it's you'd be hard pressed to find someone off the street that could tell you anything about the Sith Civil War or Malak or Revan.
A person looks at that Republic Special Forces thinks 'OOH!Stormtrooper/ Clone! I know what that is!" Because lets face it, the two big symbols of the StarWars universe are lightsabers and Stormtroopers, among other things. (BTW, did you know the term 'droids' is trademarked, and Battletech had to change its name from BattleDroids because George Lucas threatened a lawsuit?) Same thing with So people kinda are drawn into the universe there.
As far as storyline-wise, the technology being relatively similar in 4000(?) years or so between OR era and Movie Era is bogus. But as far as the aesthetic aspect is concerned, it's not totally far-fetched to think that the Kaminoan designers of the clone uniforms looked back at these Republic Special Ops people and said to themselves "That looks kind of cool! I'm inspired to make something that looks like that!"
Maybe after the defeat of the Empire, the Legacy Era Designers of the Paelleon were looking to recapture some of the old, fearsome Sith glory and were inspired to bring back that terror by designing what appeared to be an Old Republic Sith Battlecruiser.
Its not unheard of in our world. Coincidence happens--the swastika was a holy symbol in Hinduism for thousands of years befor the Nazis used it. The designers of the American presidential memorials, Lincoln most famously, used the old Ancient Greek Ionian columns as an aesthetic piece for the memorials. So it is POSSIBLE. Not necessarily probable.
Wow, long post.