[spaldingwell]

"This is exactly what it is limiting the lifespan of Facebook"

Facebook has over a billion users and has been around for ten years. No other social network can claim both of those things. Don't know if it qualifies as an example of a "limited lifespan"

[goatman]

I think he isn't saying it has had a limited life span. He is saying that it's future lifespan is being limited. Basically, he thinks it has potential to go on much longer than it will.