If they had enough subscribers to make 8 million in one year off subs (that's around 45,000 subs, btw), and all those people bought into this "just buy all the content, you'll save money!" thing, and dropped $200 for everything?
Turbine would make almost nine million.
The $200 you spend to buy all the content, character slots, etc, is the same as it would cost a VIP to sub to the game for about 18 months. In that 18 months, if they come out with (let's say) 3 new adventure packs, each of which are around 500-800 points, that's another $30-50 you're spending. And the VIPs get that content for free. Let's say they add a new race (half orcs? half-elves?), or a new class (druids?). You're going to have to pay to unlock that, too. Etc, etc, etc.
Yes, in the LONG run (as in, around 3+ years) it's cheaper to go free to play and just buy everything. However, if Turbine starts churning out a lot more content (3-4 adventure packs per year, let's say), that time frame starts extending further.
For me, $15/month is a MUCH better price point than $200+ all at once.