Drive-by spam hits wireless LANs

In some way you are right, but still I think it's even worse to use WEP
cause then the admins might think it's safe, it takes about 15 minutes
to crack a wepkey, so instead of drive-by spamming you could call it
drive-by, have a bagle, start spamming.

WEP != security, true.

The most hardware/software indipendent solution I have seen so far is
the use of VPN, simply place the WLAN outside your own LAN.

This would prevent drive-by spamming if combined with a filtering
policy that makes the wireless LAN useful only for (authenticated) VPN
access and the minimal amount of glue (DHCP, DNS to a specific
resolver) required to make the VPN work. If the wireless LAN has
access to any host you don't control directly, the risk of there being
a conduit to access the wireless LAN in ways that you don't intend
goes up.