I think it was mentioned that they will be doing two vita games a month and that gravity rush and uncharted will be sticking around for a long time, but it may have just been my fantasy and I am to lazy to read through the blog to figure it out lol.
As for how sony is making money well it all depends on how plus is done. If they do it as a flat rate for a game it actually wouldn't be that hard as the majority of the games are older titles that aren't selling well on psn anymore.
I mean lets assume there are 10k users that have ps plus (I am pretty sure it's more but lets go with that) and lets assume that they on average paid $4 per month (a year at $50 is a little more than that) thus you would have 40k per month to play with when it comes to deals and what not. So if they paid 20k for the big game giveaway, and 7.5k on each of the other two games and 5k on discounts they would break exactly even, which given the effect it is having on picking up systems/memory cards on people would still be a huge win for sony.
If they were losing money on it there is no way they would continue to add stuff to it like vita games for free, so it's obvious through their dealings they are at least breaking even, and quite frankly I think it's about perfect right now (I mean they could always add more and I wouldn't complain

) as when your customer can't believe they aren't losing money on what you are offering you are doing something right.