We probably shouldn't take "for life" any more literally than we do the "four hour workweek". It represents an idea. You might not want your boots to last forever and may in fact decide to replace them after 6 years. But if they were sufficiently well made, then you'll get more for them when you sell them and they'll last longer for the next owner if you sell or donate them.
Boots: I specifically mostly wear motorcycle boots and the tech on those is evolving quite fast.