It does worry me that anyone is driving a car with 10 year old tyres....worn or not!
This is a well argued article:
Rubber Death Aldermog's tyres will be 5 years old in September. 4 of the 5 are original, one rear is new. I'll run them through to spring 2016 and then change the lot, despite the fact they have lots of tread.
To replace 5 tyres is about £600
To replace Aldermog is about £35,000
Not really difficult to defend the decision, is it?