They do rate them for all season use,but they do wear quicker than a harder all season truck tire.Guys who do a lot of hot weather driving,or heavy hauling seem to wear them out quickly,in less than 20,000 Miles.
I use mine pretty much for winter only,but have been doing some fall and spring driving on them.This is my third season on them,and they are hardly worn,less than 10-15% worn off them.They have lost a bit of the bite on slick ice,but still way better than any other tire I've tried.I think it's like any tire,the heat cycles,exposure to the sun,etc hardens the tire,and they lose some grip.
They were cheap,cheaper than most good AT's,so if i can get 3-4 seasons,and still trade them in towards new ones (with more than 50% tread left),then I'm happy.