That sounds like a right pain in the arse. Also, where's the commercial support? A large enterprise can throw a ton of cash at Red Hat or Canonical and get 24/7 frontline assistance and deployment tools up the wazoo. There's a reason why RHN and Landscape exist, and it's definitely not to freeze second- and third-tier distributions to try and hack them into enterprise mode. You buy what does it out of the box.
And some vendors only support a small subset of distributions, usually Red Hat, as they know they can depend on the long release cycles with zero ABI changes. This keeps enterprise software houses happy, and it keeps deployment teams and end-users happy. When an update rollout can reach a cost in the six-figure bracket and beyond in manpower costs alone, you quickly subscribe to the motto that Change Is Bad.
Wow, tarballs? It's the 21st Century, we moved on
I don't know what banks you're talking about, but the banks I know of run things like Oracle, DB2, WebSphere, RHEL, Solaris, Win2K8 and AIX. If I thought my bank was managing my money using Excel, I'd run - not walk - to the teller desk and close my accounts. I don't know anyone who works ops or dev in a bank and uses a rolling release distro, it just doesn't make sense from an enterprise stability perspective. Trust me.