RDF triple assertions live forever?

Semantic Web community:

In a discussion that has arisen recently on the foaf-dev list, somebody
pointed out that they've been told that RDF triples live forever.  That 
is, once something is asserted it is considered asserted until, as it
was put, "the entropic heat death of the universe."

This seems counter-intuitive to me, as I can see plenty of data - which 
might be expressed in RDF - which changes, expires, or is otherwise
not valid for perpetuity.

Can anyone here elaborate on this?  Is it really a widely held axiom 
that triple assertions "live" forever?  If so, what is the 
justification, and how does one deal with changing data that would
invalidate a previous assertion?


TTYL,


-- 
Phillip Rhodes
Chief Architect - OpenQabal
https://openqabal.dev.java.net
LinkedIn: http://www.linkedin.com/in/philliprhodes