I think PS+ is very profitable for Sony, the Publishers and even the gamers.
I'd love to see some official numbers how many subscribers there are. Let's say there are 3 million people. In the EU it is 65 Dollars a year, but lets just say 50 Dollars p.a.
So that's a total of 150 million USD. And what they basically do is giving money to the publishers for their games which don't do very high numbers anymore. I mean, how much money do they have to invest to giveaway a game like Bulletstorm which sold like 400k on the PS3. That shouldn't be too much, maybe like 1 million USD. Peanuts for the PS+ money pool, but free money for the publisher. The only really expensive deal was Red Dead Redemption, i think Sony had to pay good money for it, since it is a real blockbuster and still sells well.
PS+ is an awesome value for the gamers, and everyone should participate. Heck, the more people get into it, the more value could be added (to sonys wallet, too).
I doubt Sony gave them any money (I hope) in the case of First party games obviously they own them so that doesn't matter. But for games like Red Dead they reduced the price of the DLC when it came out so people think oh i'll buy the DLC (Instead of buying used then not having money for DLC) so everyone wins, consumers have Red dead for free, Sony and Rockstar get money from the DLC sold.
In the case of Borderlands the DLC was on sale but it was clearly to get people excited for Borderlands 2. But for new release PSN games I would not know how that would work?