Here's the Metzeler warranty info.  Kind of Greek, imagine they do a one off on a condition like you show.  http://www.us.metzelermoto.com/media/metzeler_2006.pdf 
But it might help to see what I found on Goodyear's policy too.
Here's a site that explains Goodyear's position on weathering and cracking.
http://www.goodyear.com/rv/tirecare/tire_age.htmlAlso, the explanation, and the way they adjust tires on warranty maybe Metxler's is similar or should be:
Weather cracking, picture attached, is a naturally occurring condition that results from exposure to heat and sunlight. 
Goodyear's warranty for weather cracking is four years from purchase date (or four years from manufacture date if proof of purchase is not available). Weather cracking is common in RV tires from all manufacturers.
Appears as crazing and or cracking in the flex area of the sidewall 
Probable causes of tire weathering 
Long periods of inactivity or storage 
Direct exposure to air and sunlight 
Tire age 
Exposure to high levels of ozone (smog, electrical generators) 
Excessive washing or dressing using alcohol or petroleum based cleaners 
When should the tire be replaced?Cracks > 2/32" deep Internal components of tire (steel or fabric body plies) are visible 
Without evidence of weather cracking, use the following as a gauge:
Usage per year --More frequent usage will result in longer life 
Vehicle storage practices (6 months loaded with little or no rotation is not good!) 
Casing quality --Absence of repairs, liner wrinkles, weather cracking, sidewall scuffs or cuts