Linus's public key on 100000 computers!
If someone finds Linus's secret key, all those computers could be fooled into thinking Linux signed some source code that he didn't! Even worse, type:
gpg --recv-keys 79BE3E4300411886
and you get a copy of Linus's public key, and something similar will get you anyone else's (if they have one). It is almost as if public keys were available to anyone!
The routers have two obvious uses for ssh keys. One use is for authenticating the router - in which case the same secret key is on every router. I could copy that key to another device, and the telco could be fooled into thinking they are talking to any one of their routers when they are really talking to my laptop.
The other use is for remote administration. Each router could have its own key. When the telco does an update, the computer doing the update needs to know the secret key for every router. If a cracker can get one, she can get any or every secret key, so having only one key does not remove any security.
What is the issue here?