There's actually a variety of things that contribute to the overall stability of our game servers, which have improved steadily since the days you speak of, G.
Improvements and patches from Bioware fixing many of their problems has helped a lot. Understanding what was causing crashes in the past has also helped. Things like disallowing the old seamless cross-server portaling (where you wouldn't have to connect and log in again), spreading out the time it takes to load housing furniture and other such things. Reduction in lag from various causes has also brought significant improvements
Some changes from Bioware have also allowed us to improve the quill system in such a way that was more "friendly" to the server in that we no longer needed to use an external utility to alter the data of items in-game.
Anyway, it's been a constant evolution over the years and primary credit really goes to orth for some of the more significant improvements in stability and identifying the points of contention that would lead to lag and crashes.
Having fewer people doesn't hurt either, but we have had similar stability with more people for quite some time.
