I imagine its because they have gone offline since the search results come up, what you must understand is limewire is searching many thousands if not millions of pc's worldwide, so people are going on and off line constantly. Sometimes people will cancel your download from them for various reasons as well, this will also show more sources needed.
As a Limewire user, I have a question. Does anyone else find that when they download from Limewire, they usually also get lots of spyware and adware too?