I think the investor explanation makes sense. F2P games are not made for long term sustainability. They're there to make a quick buck. At best, you'll get six months to a year out of most of them, and then a year later, they're forgotten.
But if you want to build a high quality game with long term content instead of a bunch of freeloaders hanging around for six months, a P2P model makes more sense. SE is playing a long game. They'll never be able to reach WoW, but if they can reach the success of XI, they'll be okay.