I got my XTerra in the fall of 2005. I only have 36K miles, and the tires aren’t bald, but I didn’t feel comfortable in the snow with the original tires. For some odd reason, probably to save money, the original tires were not really suitable for Oregon in the first place. I’m much happier with my new tires. They have an aggressive tread and are “siped” to increase traction in the rain. Siping [Seyeping] is a pattern of small slits in the tread.
One of the pictures below is a demo of siping at the tire store where two samples of rubber, one siped and one smooth, are dragged across a smooth surface that has water on it. It take much more force to pull the siped sample across the surface. Siping is not a new process and you can see some very minor sniping in the original tires, some of which is picking up gravel chips. But you can see the new tires are much more aggressively siped.
Click on a picture for a larger view.