It depends on who's online at the time of your search..files available are constantly changing as users log on & off. It also depends a bit on the ultrapeers that you're connected to. You can't search the whole network...it's way too big. So you connect to ultrapeers (people with fast connections, who aren't firewalled), who connect to other ultrapeers, who connect to other ultrapeers etc etc & that lets your searches reach a certain amount of the network.

Click on LW's Connections tab. Right click on the ultrapeers you're connected to > remove. Once you remove an UP, a new one takes it's place & that can change the search results that you see.