I noticed this very well.
About 2 years before the postings seemed to have been stored a little bit for all those Facebook friends who didn't get a chance to see it right in the time you were posting it.
So they got to see it later on and they also "liked" postings more than today.
On the one hand it will be of course a monetarization attempt of facebook.
On the other hand many people in these days post pretty important stuff about the corruption and the big crimes of their own governments, politicians, bad banks and really dangerous profit-over-life companies.
Leaders of the world with bad intentions fear such an awareness of the people and facebook just like the internet are media that can spread those informations very fast.
So I guess they made some kind of filter for informations where much important stuff goes through unseen.
The weekend before thousands of people from the tea party movement united via facebook to organize a shutdown of the government in Washington (guess it were about 500000 people).
It was such a great movement, that somebody had shut down their facebook page.
They made a new page though - but with that you can see another possible purpose of this facebook topic.
Informations can cause revolutions (which are necessary from time to time) which "mighty" people/tyrants may fear.
If you post something you want others to see (or to listen to), leave it for a while (a month or so) without posting anything new in this time.
Good friends, interested people and subscribers will take a look at your facebook page from time to time.
Patience is the mother of reaction (or sumthin' like that). )