Concerts in the Bay Area

What is it about the Bay Area that it is so easy to find last minute below cost tickets to hot concerts? Or is it just a sign of the times and technology? Having just come from Toad the Wet Sprocket where I picked up $60 tickets for $30, and earlier Coldplay $112 for $75 I am floored by the cost and availability. Makes me wonder whether the Projekt Revolution tickets that I actually bought during the presale were worth it. Of the last five concerts I have been to, four I picked up tickets from Craigslist below cost within the week before the concert.