To the same extent though - if free games are encouraging you to buy sequels/sequels - would there be a percentage of people out there who sign up for Plus (I've got casual/ non-core gamers in mind here - not people like us!), with the intention of mainly playing the free/subscription subsidised offerings?
"Yeah I loved playing Resident Evil 5. I'll just wait a year or two til 6 shows up in my plus offerings. Hey, I waited that long to play 5, so a coupla years wait is no big deal. Besides I pay for plus, I've got at least 16 games a year in the pipes to play/complete, I may as well wait."
It's just a thought, not a strongly held belief. But it seems logical. These people may have been the sort of people that just buy used games (no revenue to publisher) or few games (less revenue to Sony than Plus subscription fee) anyway, and then whose to say they're the sort of market that would pay for a plus subscription anyway.
I know Steam sales have conditioned me to passing on many impulse buys, awaiting that inevitable %30-75 off Daily Deal or Black Friday sale. And even though my cable channel usually gets its "movie channels" (ie. Not pay per view/digital rental ) titles about a year after their dvd release, but for plenty of titles I have casual interest in, that I'd maybe rent, or wait til they're $10 or so, I'll think - Nah I pay my monthly cable fee, I may as well wait a few more months. Not the titles that I "must have" (got Dark Knight Rises last week!) but those second tier "maybe want" titles. But hey - sometimes I end up buying those too if I really like them so...
Demos generate more sales, no doubt. Do free/subscription package games generate more sales, or encourage a " my sub fee will cover it" mentality. Overall I'd say its hard to accurately quantify. I'm sure Sony will/have/continue to undertake user/market research to determine this. I'm sure Microsoft have/are looking into it as well, if not Nintendo - heck, I could call the extra I paid for my launch 3ds and its 22 free titles (I'm including excitebike and 4swords too because - they were free in that time frame as well) a one time 3ds plus fee! And I will admit hours spent playing Fire Emblem or Warioland, may have been spent playing other games I'd planned to buy, but even I couldn't say how many... I know I'd definitely have bought a few of those titles from the e-store...
Anyway, just adding a few different shades and talking points to the discussion, no big points to make..