I've been able to successfully crack wep on a old linksys router i had using the method described in xploitz videos.
I went to visit my cousins house and tried to crack his wep encryption as well. Either i didn't do something right or this router didn't like to produce any significant number of ivs. Of the packets i injected over an hour period i only got about 1000 ivs. The router he was using was an old dlink.
After seeing this i remebered reading about some routers that had updated firm ware that didn't produce weak ivs so they weren't easliy crackable.

Are some routers using wep just not vulnerable to attacks or am i crazy?

thanks for you help