Rosetta stopped working in a virtualized Snow Leopard hosted in Mavericks (Parallels or Virtualbox)
it turned out that the type of the hard disk I initially chose for installing Snow Leopard on matters.
So, when creating the virtual hard disk drive in VirtualBox, selecting a "hdd" Parallels type file, was the key. I tried with VDI, and VMDK (VMware) but all installations with these lead to a sucessful install of Snow Leopard, but a non-functioning Rosetta.