Check the installation guides and you will notice that the only difference between the software owner accounts is the group; you can argue that "Oracle" recommends...blah...blah...blah...

Also, for example: for 10g Grid control to work to it's "fullest" (centralized deployments, patches, etc...), all Oracle software on a particular server (node) may need to be owned by the same account. There may be work-arounds, but it would make things harder to configure and manage.