If that's really the case then there's no way Facebook is worth what (most) people think. Instagram launched in October 2010 and were acquired with only 13 employees. If a tiny company like that even has a chance to dent Facebook's market position then they are in an extremely precarious spot, IMHO.

More startups like Instagram are going to appear. No one can predict when or where but given the low barrier to entry, it's going to happen. If it costs Facebook $1B per "bullet" to kill them then they are going to run out of bullets.