Host caches and peer lifetime

Sorry if this has been covered before - do UDP host caches and
gwebcaches return a uniformly random selection of known peers? If so,
and if we can assume that peer lifetimes follow a distribution with a
heavier tail than the exponential distribution (ie old peers can be 
expected to live longer than young peers), then would it make sense to 
return old peers with higher probability than young peers?

Thanks,
Michael

http://people.cs.uchicago.edu/~matei/PAPERS/ic.pdf
http://2003.iwcw.org/papers/bustamante.pdf
http://www.imconf.net/imc-2005/papers/imc05efiles/stutzbach/stutzbach.pdf