Well I am not sure I buy that only 60% of X360 owners make an account of any kind (because isn't any account=silver?) is that even possible (EG, use an x360 without a silver account?). that havent even been turned on in a while is going to be MUCH higher than for X1/PS4.
The 60% figure is derived from numbers directly reported by Microsoft. Lots of people never hooked up their 360s to the internet because they didn't have WiFi built in for so long.
MS does provide free games for XBLG. In fact they are truly free. Even if you cancel your XBLG subscription you keep the game. Im not sure if thats the case with PS+ on PS4. it wasn't like that on PS3. A free game was REALLY a free game on XBLG.
Yeah, one free game at a time, two per month, most of which have been over 5 years old. PS Plus gives you access to 17 games on your first day as a member, many less than a year old, some brand new, and you get at least one more game each week for an entire year. It's not a shock people see the Instant Game Collection as a far greater value even if they're just long term rentals.