Because the users you are connected to don't share these kinds of files. I dld files averaging 3Gigs these days (albeit, not in LW, sorry), but can you imagine waiting for that kind of file to come?
... What if you have a modem (or a modem user at the other end)? That wouldn't just take ages...
Anyway, what I wanna say is that if anyone puts up a file larger that 1G and they are close (or connected) to you, then you should see that file in the search results (provided you searched for that, of course, duh)

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

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