Is router uptime a measure of stability or insecurity ?

I was reading Cisco Packet Magazine the other day, and noticed a few mails from readers claiming that they have many Cisco routers in their network running continuously for more than 3 years. The continuous long uptime of a router shows stability and reliability of the specific hardware, but on the other hand it reveals also an insecure network.

A router running continuously for many years, means that it has not been upgraded at all. A router which has not been upgraded for more than 3 years, it probably runs IOS versions 12.0 or 12.1 which are full of security vulnerabilities. I would rather have a network with router uptimes of less than a month, but with all latest Cisco IOS security patches, instead of having a network with router uptimes of 3 years and full of security wholes. What do you think ?