The German view on warrantee, and this is true of most German brands, is if you fucked it up it's got to be your fault as they don't make tools that break if used in the manner for which they were designed to be used. It's a totally different mindset from the American point of view which is no matter how much I abuse your **** you should still give me another one. I think this attitude came from Craftsman having such a liberal return policy during their run at Sears. The continent in general, and the Germans in particular, do not believe that you should be rewarded for abusing tools.
That is true, and not only in Germany. As a matter of fact I only know of the UK and USA who have these kind of life time warranties. Everywhere else (that I know of) you get a few years (or none for consumables) or a limited life time warranty at best. The fact remains that any kind of defect caused by natural wear, misuse or abuse is not subject to warranty. It'd be like buyng a bottle of coke and dropping it, the glass shatters, and you demand they replace it. You drink the coke and demand a refill till the day you die, and other absurd scenarios.
The 2 main things you can claim warranty for are:
Visible defects right out of the box like wrong dimensions, deformities, dents, lack of material, lack of coating/plating, rust etc.
Quality issues due to some error in the manufacturing process (forgot to heat treat, the steel alloy batch wasn't good enough etc.)
I had to send back pliers wrenches. It was the latter category, probably didn't undergo heat treatment and was too soft. This is what the first bolt I ever used it on did to it:

I asked people on reddit and even asked the local rep of the country I live in and everyone said this shouldn't have happened so I returned it and got a new one.
Having said all that...
I chipped the first 1/8" of the end of both blades . I dropped them off at the store and after a couple of weeks the representative came by . He said I used them wrong, I was supposed to cut at the bottom instead of the end. That sure sounded like an excuse to deny warranty to me.
He was totally right to deny warranty due to misuse. The boxed versions come with instructions (to do it in 2 steps - unless it's the version with the grooves that won't let the bolt slip to the front) and they have videos and pictures on how to use them correctly on their website. The tips are only used for the smaller stuff like in this video
Overall I'd say Knipex has excellent warranty for defective products.