Hmm, great companies fire 10% of their staff each year? I have never read that anywhere; can you point me to you reference?
Try searching your own union's site Litebulbs.
http://www.unitetheunion.org/pdf/(JN...20Briefing.pdf
It's fairly common in the IT industry (e.g. IBM, Oracle, etc), some merchant banks, GE, Enron, etc. Can't say I agree with it, but if you're going to fire anyone then surely the worst performing x% would be the first target?