Don't forget that word of mouth is the best advertising you can get. If they had closed down servers or kept charging people would be raging harder than they are now and thus leading to more hate towards SE. Even if they shut down the servers and opened them back up 1-2 years later you can bet that no one would pay to play and most would never even return to check it out with the next gen MMO's coming out. By keeping it f2p they're getting the 'free' advertising they desperately need from patch to patch by people simply discussing the game on numerous forums. I assume they're also betting people will constantly return to check the game out if they can freely invest a ton of time into their game and build their characters. Say 1.18 is a big hit. Everyone across all these forums will be saying "FFXIV is a ton better now, it's the perfect time to return!". By those discussions alone you'll have people dl the patch and return and even some new people go pick up the game to try it out. Just saying that they're not making it F2P without having something in it for themselves.
On a side note, it's not just the $80 that people are pissed about loosing at launch. It's also large number of people who, by looking back on XI and loving all that it was, thought XIV would be the 'new XI' and ran out to buy a new PC to be able to play this game in all it's beauty(remember those high ass system requirements?). SE hyped up launch and it failed hard. Now all these people are out 2k~$ on rig for a game that sucks. I spent that much on a new PC too but I use it for other stuff as well so it wasn't a huge loss for me.