Those are version numbers of the ssh protocol supported, which vary separately from the version of the actual software in which they're implemented.
There are two versions of the ssh protocol in use today: 1.5, which is very old, and contains some integral security flaws, and 2.0, which is still several years old, and believed to be secure.
The version banner offered by an ssh server usually includes both these sets of information. The protocol version is what's used for the client and server to negotiate which protocol they'll speak, and the software version is just informational. So you'll see something like:
SSH-1.99-OpenSSH_3.4p1
1.99 is the version announced by a server that's willing to speak either 1.5 or 2.0, as the client prefers.
Please forgive me if you already knew all this, and just wanted to know why it'd be different between two machines of the same distribution version. That would happen either if one of the machines had had its sshd_config file modified to alter which versions it supports, or if the host key used by one version or the other was invalid. Invalid could mean missing, or having permissions which are too loose; openssh will refuse to use a key which is widely readable or writeable.