Honestly, I think anyone asking for HP-UX or AIX "because it's UNIX" should have retired at least a decade ago.
Similarly, anyone naive enough to believe that "Any skills, staff, source code, infrastructure, and solutions you invest in any Unix are portable across IBM, Sun, Fujitsu, HP, Apple, and generic 32- and 64-bit x86 hardware." really shouldn't be placed in a position where they have any say over platform choice.