I agree, it was a great book, as was Watership Downs. Maybe not everyone's cup of tea, but I enjoyed both immensely. I didn't realize Adams was the author of both... thanks. It makes sense. He has an uncanny ability to humanize animals.
I think Adams ended Traveler that way as his statement on war. There was glory in it, and bravery is much valued but in the end, like Traveler, the innocent beast who was a tool of war and never understood it, maybe like some men in war are too, war is in the end, sad. Adams in both books finds a way to glorify bravery and heroes, but in the end, he hates war as it is awful, and should be hated. The ending of Watership Down was not disimilar to Traveler. The heroes all died, but are remembered and revered fondly.