I would expect all CF and SD cards to work in all cameras, but not all at the same speed obviously. The fact that only SanDisk or Lexar cards seem to be guarenteed to work means to me that this is more of a Nikon issue.
When standards are created there are many MUST and MAY statements when it comes to vendor specific implementation. To get certified all the MUSTs, well, must be met. The MAYs is where you get into a grey area of a specification.
It may also be that the D4 has a single I/O bus controller that is designed around the XQD and has the CF slot in compatibility mode. There may be things in the XQD spec w.r.t. CF compatibility mode that are not supported, partially supported, etc.
If you expect all cards to work in all cameras you will forever be disappointed.