Normally I'd agree with you on that one Boost. Those two characters are very obviously imitations of the two characters you mentioned, and yes, that is pretty lame. Though sadly, those two character kick the total pants off of the Darth Vader and cheap Boba Fett knock off (Jango is his name-Oh) that appear in the prequels.
As for the no obvious reason part, I am going to have to assume your computer doesn't have sound... the Darth Vader knock off narrates and explains that the Sith have been waiting to take down the Jedi for three hundred years, growing in strength while the Jedi grew proud and lazy. Star Wars has always (or at least for a very long time, can't remember when it actually first appeared in print) had a back story of wars in the past between the Jedi and the Sith. Knight of the Old Republic takes place during these times, some hundred (am I right on that? Or is it thousands?) of years before Star Wars.
Sure, I suppose you could see this plot as a bit silly, but I'd be rendered speechless if you tried to tell me you found the nonsensical plot of the prequel trilogy more reasonable: Palpatine and Darth Sidious both lead armies in a war against one another. Palpatine and Darth Sidious also happen to be the exact same person. He has his two armies fight one another in order to... well, in order to... you see... err... well... he has his two armies fight one another. Neither side knowing that the armies they fight are essentially lead by their own behind the scenes leader, and this war goes on for year and years and year, until finally he convinces the universe, with the endorsement of the village idiot turned senator, to appoint him as their leader. More years and years and years pass, and he announces himself dictator, and then ends the war that very same evening and lives happily ever after... until his best friend murders him three movies later, after which all his loyal followers instantanously decide to give up, which puts an end to all the galaxies problems, making teddy bears all over the galaxy sing with delight.
I dunno, but for some reason I'd take guys with red lightsabers vs. guys with colorful lightsabers over CG New Zealander clones (with a few obnoxious indivisuals with colorful lightsabers and goofy costumes thrown in for good measure) vs. hoards of cheaply manufactured robots any day of the week.