Nice try with the "we tried to get these dogs adopted" bit, but did you hear a word about this up until now? Had the company come out with a press release saying 100 dogs were going to die unless people stepped forward to adopt them, there'd have been homes found. If we can send hundreds of rabbits to rescue projects in the U.S., surely we could have found placements for retiring sled dogs.
Here's a link to the blogosphere heating up over this one. A measure of just how big this story is going to be: I did a Google search on "sled dogs killed" and quickly pulled up search page after search page of news coverage, blog comment and tweets on the Pemberton dog massacre.
Just in case you're thinking this is some kind of anomaly in the dog-sled-tourism business, a 2005 story out of Denver, Colorado notes a similar shocking slaughter south of the border.