My point exactly. I'd have likewise countered with "it was already at 11 million by the end of Burning Crusade, Wrath literally did nothing but add 1 million subbers, & then sustain that 12 million mark for a long time. Hence, obviously, while they did do good with Wrath, it wasn't the same "ground breaking" thing that Vanilla & Burning Crusade were."
The problem is the actual statistics are overshadowed by the whole "Sub count peaked during Wrath (12 million), & then held steady until Cataclysm." That's all most people focus on, not Expansion growth, or whatever, just that, single, specific fact.
As for the crystal ball thing - by late 2008 the VG Industry as a whole was already moving towards "casualisation," & I think that had an influence on Wrath's development (Activision merger). It's likely Blizzard was piss-scared of falling behind the "curb" for years on end until the next Expansion Pack came out, so instead of risking their star IP on what at the time was (& continues to be, to this day - in a different form) perceived as an ever-shrinking "core playerbase" in the entire Industry at the time (PC Gaming is Dead/Dying/etc.), they instead opted to slowly introduce casuals to WoW instead. Then, once they realized how interested the afore-mentioned casuals actually were..... see post-Ulduar Wrath.
However, I do give the "anything would have worked" argument slight credit. It's true, Blizzard had both a hell of a lot of wiggle room, & none at all at the same time with WoW's future. They could have done a lot, & the community would have given them a chance, simply because at the time, we had blind faith in them. Everything they'd done up to that point was near-universally awesome. Hell, until post-Ulduar, even Wrath was doing just fine with most people. Wrath's fucked up Launch Raiding stuff was overshadowed by the leveling experience & the rest of the content for most people, & then of course came Ulduar, which set Wrath "right back on track." Then they started with the Trial of the Crusader stuff, the LFD Systems, etc. & everything started going downhill, permanently.
If they'd sustained the amount of "casualisation" to manageable levels, as with 3.0/3.1 Wrath, instead of like with 3.2/3.3 Wrath, then they'd have still managed just fine IMO. It would have forced them to create a real balancing act between Hardcore & Casual, which with some effort they could have successfully maintained over time. Unfortunately, we all know how bad Blizzard is at long-term vision & balancing, so of course, the inevitable happened; they got greedy.