Hi tonex,
You are technically correct, you do not necessarily
need 2 IPs for your VPS as everything can run off of one with little to no problem. All I have ever done with the second IP is put my second nameserver on it. But you could use it for a dedicated IP for a one of your sites or run SSL on it too.
And no, both IPs are assigned to the same VPS.
Pretty much all VPSs or servers come with a certain number of IPs. Knownhost is generous and gives theirs 2. Doesn't mean you have to use them or do something special with them
