The reason that they had so many full servers on "release day" was due to their launching the game on a progressive scale.
For the million or so pre-order copies, users were allowed up to 7 days of early access. The earlier you adopted to the pre-order, the more free play time you could receive. I personally was allowed a jump-start of 5 days' time, leaving my main character at level 27 [of 50] at launch.
More importantly, this early access transitional phase allowed Bioware to not have to concern themselves with overpopulated servers, as they could launch more as needed during scheduled maintenance days, today being the last of them. Additionally, this allows users to not feel crowded in earlier leveling areas, and everyone got their fair share of monsters, World bosses, and item interactions. never must you wait more than 30 seconds to pick up a quest item -- even if the jerk right in front of you just stole it, while you conquered the big bad that was in your way.
It's a nice title, with a very strong launch, and to be honest, I'm surprised that we haven't seen Sythe.org pick up on the [more than] 3 million copies shipped to date, and start building those market forums.