I understand that , I just don't see it in the config . If you have to replace the device how does it know to create the key from the config file if there is nothing in the file to say to create it . My question i guess , after loading the config file into the replacement supervisor or router do you have to manually add the "crypto key generate rsa" command as it does not show up in your running config. Maybe I am missing something simple here.

There you are, u may have to generate the keys separately on each device.

how different is "show crypto" commands on the 2 routers.

however,on high end routers/switches When you use the redundancy force-failover main-cpu (Catalyst 8540 MSR) command to manually force the secondary route processor to take over as the primary route processor the SSH RSA key-pair is automatically generated on the new primary route processor. This ensures that the SSH server is enabled on the switch router even after route processor switchover and allows you to start configuring the new primary route processor using a new SSH connection without reloading the switch router. (content taken from whitepaper)

I think I found my answer , the crypto key is not stored in startup config , it apparently stored in the private-config file in nvram so that does not get saved so when you config the replacement device you will have to manually config the keys again with the crypto key generate rsa command.