and this is why TF2 will be on the PS4.
MS had enough money to do it for the first one since the install bases aren't low, but that PS4 install base will be too big to ignore the sequel.
This is EA we're talking about and Respawn wants it on the 4.
Identifying the Xbox brand with the game was important and that is what this move does. Even going forward (barring a major difference), with the game being multiplat, it will still be heavily marketed and identified as an Xbox brand game.
Also, Respawn sold their publishing rights to EA for the game, so that's why EA had the control to do whatever they wanted with the IP. That's not in place for sequels. EA did fund the startup of the studio, so almost like a rapper, Respawn gave up that publishing for the first game.