Okay let me try this again since people don't seem to get it. Not that it makes any difference because posts with actual information seem to be overlooked.
Look at the numbers from previous expansions. Look at the first day numbers, and then look at the first month numbers. See how the difference isn't all that huge? Most people who buy the game in the first month buy it on release day. That's what you can get from that. WoW now has fewer subscribers than it did at it's peak. MOP can be the best game in the universe and it's not going to, on release anyway, make ALL of the people who left come back or bring in enough new people (Because lets face it, WoW as a game is hard to get into even with the first two expansions bundled with Vanilla) to close the gap between the end of Cata subscriber number and the peak number. Thinking otherwise is illogical and it's just dreaming. Thinking that MoP selling fewer copies than previous expansions means that the game is boned? That's also just dreaming. Comparatively the numbers are impressive. WoW has aged well, that can't really be disputed, not even by me on my most bitter of days.
If WoW was a dying game it speaks volumes about the rest of the genre because it just blew away it's most powerful competition. MoP is a success, there is no other way to look at it unless you judge "Success" to be regardless of subscribers it must sell at least as well as WLK. In reality though it doesn't have to break records to be a success, I'm sure Blizzard is happy. I know corporate is happy. I'm very cynical, and MOP managed to get better first week sales than I thought it would. It has impressed me.
Now we need to see the numbers for the first month, which we can be pretty sure will be a bit lower than previous expansions, though most of us were sure of that before the expansion even released. Then we'll need to see the quarterly report and then the next quarterly report after that to see if Blizzard has the subscriber leak patched or not. Speculation on this subject at this point is really counter productive - Just look what happened with SWTOR. BioWare/EA posted very strong release numbers, didn't say anything about a major population drop off (Although all of us playing noticed it whether we wanted to admit it or not.) and then when they did release those numbers woops there went the vast majority of their subscribers despite speculation that the game was extremely strong.