Pet server classes is a much nicer concept anyway. I never liked the instance based personalization. Creating a machine, defining its class, and seeing it become a machine of its class is magical.
Of course, the newest idea is for creating and destroying machines automatically... that outside of the could is quite pointless but people want it anyway. I imagine seeing all that orchestration working must be even nicer than a machine autoconfiguring, but I am yet to see a place where it just works.
One argument for "cattle" servers on bare-metal is security. Being able to reset the machine to a clean, known-good state would clear any leftovers including potential malware. Having machines provisioned from images that include everything they need to run also means you don't even need to grant anyone root access (which you'd otherwise need to be able to audit so they don't leave anything malicious in there).
Of course, the newest idea is for creating and destroying machines automatically... that outside of the could is quite pointless but people want it anyway. I imagine seeing all that orchestration working must be even nicer than a machine autoconfiguring, but I am yet to see a place where it just works.