Alright, yesterday I got a Lumia 800 for trial, which meant I had to compare it with my 4-month-old N9. So I removed the rubber cover & I found this. The matte layer has indeed worn off. How? It's my own fault because I hadn't removed the cover since a few months and it definitely hasn't coped well with the sweat and heat while inside my pocket (I live in a country with a very warm weather). Clearly, Nokia haven't tested it under this extreme weather condition.