Well, the people developing the ZFS Storage Appliance care and so by proxy the people buying it because let's face it the ZFS Storage Appliance is called so for a reason: ZFS.
And that's what the people care for. And in enterprise quality ZFS is pretty much bound to Solaris. As the ZFS Storage Appliance is x86 , any idea of reducing Solaris to SPARC is somewhat problematic as well. It seems many products are interwoven at Oracle.