First off, let's keep the comparison between the two games strictly to the vanilla release versions. Expansions have a specific theme to them (i.e. Illidan, Arthas, and Deathwing) whereas release is more general. WoW started with MC and BWL and their main story, but once those were cleared on a regular basis, the had to add new raids. SWTOR started with EV, and now that that has been cleared plenty, they added new ones.
Nothing is different except the mentality of gamers of 2006 and now. Back then really tough raids were just how things were and we accepted that for what it was (and most of us liked the challenge). As time went on, business kicked in and started dumbing things down to allow lesser skilled players experience the content they spent a lot of money creating. Now it's 2012 and Bioware can't revert to vanilla WoW difficulty or else it'll still lose subs to scrubs and casuals. Hence the reason for NM and HM.
IMO, people are impatient and excepted everything at once. If you think about all the things people are crying about that need to be added to the game, almost none of it existed in vanilla WoW. So why then didn't vanilla WoW suffer 25% sub losses? Think about it.