I've flown in the back and in the front of plenty of 25 + year old MD-80's, and I can count on less than one had the times I've been stranded 'cause it "broke".
It 'aint about buying "older planes". It's about how you run a company.
You are talking apples and oranges when you are comparing a 25 yr old airliner to a 25 year old biz jet that gets worked almost as hard as a airliner.
The fact of the matter is the biz jet will break more. Now don't get me wrong I think the mangement is incompetent, but biz jets aren't built to take the pounding of a airliner.