Galileo
The "what can we get for free" is not limited to FB, it's a www wide, SL wide, world wide issue and it's caused by and large by merchants and freebie websites who are trying to capitlise in an economy and using the fear of spending in their favor to then sell advertising space in return for high traffic)
SL is almost notorious for the freeloading culture thanks to the imbalance of people selling quality content to people giving quality content, people just "expect" a freebie or at the very least greatly reduced. But again, this isn't limited to SL its the effect of a recession on the net.
This is the first time the internet has faced any form of economic collaps of this magnitude and we're seeing the merchant/consumer changes for the first time in history.
I have 2 websites one did offer texture stock for free (at the lowest resolution) we had 2000 members in less then 12 months and over 2000 texture downloads a month (of the free textures) For one of the higher resolution images they would only need to spend 1 dollar and we did allow commercial use., well needless to say very few people spent money, no one said "thanks" and so we pulled the plug on the freebies.
Regards FB - people do spend money on FB not sure where your getting your information from but there are game companies investing time and money into making addictive and "user to user" competitive games which encourage players to buy "gold' (or what ever) once they are addicted.
And of course more residents = more content creators, but the ratio will not be in the content creators favor, most FB users are just people who want to socialise online, share photos, compete with their "friends" in Farmville,(why?? lol) upload videos from their mobile phones, flirt with strangers and so on, so having the ability to own their own 3D appartment , play "dress up" and invite their FB friends into a 3D space would be very tempting and again, free...
Where ever LL advertises there is always going to be a certain % of sign ups that decide to be a merchant, not sure why you think FB would hold a higher % in that regard to any other area.
Look at IMVU - see how many people are logged in and then ask yourself why because it isnt the client, it sucks, Ive tried it. ( cartoon avatars and environments, no freedom to do much of anything other than jump from one targeted seat to another targeted seat ) but that aside they have been very clever on how they run things.
Quote "try attach a subscription fee to FB and watch people leave like the tide rolling out"
Well, yea if its compulsary but that would be the same for SL or any other service that initially allowed free access.