There are actual close friends, and then there are people you know or care about to some degree. Dunbar's number (somewhere between 100 and 250) describes the latter.
That may include extended family, neighbors, coworkers, your acquaintances from hobbies/bar/church/whatever. They're not all close friends or immediate family, but still people that you sometimes interact with, and might want to contact.
Not really care for, but the number of relationships you can keep track of:
"By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships."
I wouldn't say that the figure of Facebook friends is an indication of number of people I really cared. I do care some of them (sometimes sending wishes for them), but a majority of them are either my classmate in high school, a junior in university, a (former) co-worker, or someone whom I met in social gathering that shared common interests and wanted to hear/talk with them. It's like the use of Facebook as a directory since everyone has one.
Conversely, there are plenty of friends whom I know personally, but did not connect via Facebook (we use IM for that). This may probably be counted towards the close friends I really cared for; only few (no more than 10) people fits this criteria of mine.
At the time I deleted my Facebook account, I had a total of twenty friends. And all of them were people from where I moved away from, or people that moved away from me.
Family, and local friends, I did not friend on Facebook, because I was going to see you anyway.
My mom asked why I wouldn't 'friend' her, and I responded that I talked to her on the phone for 60-90 minutes every single weekend. Without fail. Plus, I used to snail mail her printed photos on a regular basis.
When she died, I found two boxes crammed with every photo I ever sent her.
