What defines a really good systems architecture?

whether network, operating system or processor architecture, what defines a really good one, is that no matter how much stupidity is thrown on top of it (whether its unix, the internet or RISC) it mostly survives intact -e.g. people added X to Unix, BGP to the Internet, and floating point co processors to RISC, but they still didnt manage to completely break them

this was promopted by watching yakov rekhter's google video tech. talk about 18th year of BGP hacks with what I would say was a remarkably consistent 10% inability
to abstract

(as in Cool Hand Luke: "what we have here is a failure to abstract")

so there