You know, you get what you pay for.
The Limewire people have no control over what files people are sharing. To do so, they would have to download it, scan it for viruses, and then somehow put a "seal of approval" on it. It's much easier and efficient to let the "buyer" beware, in this case us downloaders.
I very seldom if ever download executables from P2P. The few times I have, I've immediately scanned it for viruses at
www.pcpitstop.com, and maybe one out of four files was virus free.