Pretty much this. Not only is it costly to bring in an actor in case of a change of plans, it's also logistically difficult sometimes to fit extra sessions in.
And just because there are sound files included doesn't undermine or disprove what Patrick said. He indicates that it was an ongoing discussion and informed by feedback BW has received about LGBT content/tropes in their games. As they don't always have the luxury of adding VA, it's better to record some lines that they're more than likely not going to use than risk a situation where they decide to reverse their first decision and then need to somehow get those lines recorded.
I read a really interesting article (in regards to the SAG-AFTRA strike, actually) by an anonymous game dev who says that voice work is always per day. So it's not per hour. Imagine you had to pay someone $10,000 to come in and say two lines you forgot to have them record them the day they came in. It's nuts.
http://askagamedev.tumblr.com/
It's some ways down.
It's a good read, and gives both sides of the disagreement. I know this isn't exactly twitter news, EP, so I'm sorry, though it IS a very hot topic on twitter within our social circles right now so it's kind of topical.