I'm guessing they do that because they are promoting "local" deals and not online ones. I've had a couple of instances where I've inquired about CL postings less than 2 hours from me but as soon as the seller found out I wasn't "local" they refused to even give me more info... I guess since I wasn't right in their town they thought I was some sort of online predator or boogie man or something...
wow, these people have been watching too much TV maybe. Like all the locals are law abiding citizens, it's those crazy out of towners you gotta worry about;)