I think i read sometime that Massad Ayoob said that a Glock 22 had a service life of about
20 000 rounds, is this true?

Chuck Taylor on his G17: The pistol about which you inquire now has 226,000 rounds through it and is still functioning normally and shoot into 2-inches at 25-meters. I did, however, replace the extractor at 200,000 rds.

Are the differnce that big on 9mm and .40SW wear and tear?

Quoted: Are the differnce that big on 9mm and .40SW wear and tear?

If 20k were the case my G24 would have worn out 3x already.  

Just shoot it until it breaks, but please leave it in your will to me  

OK, but the slide on the 24 is longer and heavier, which doesn't give such a high velocity on the slide?

But maybe Mr. Ayoob was talking about the barrel life, not the whole gun itself. Anyway I have both G17 and G22, and if my G22 stops I have backup

Quoted: Are the differnce that big on 9mm and .40SW wear and tear?

I would expect so.  The .40 is much more punishing than the 9 or .45 acp.

I would hope that you'd get more than 20k out of one though.

I wonder what is meant by "service life"? Parts are going to wear out on any firearm, I wonder what parts are wearing out at the 20k mark that deam the pistol unserviceable.