AMD’s beta4 SDK has fixed the decorated naming problem. They now have clean naming and stdcall functions, analogous to OpenGL. So I think the AMD SDK in its current form is ‘correct’.
nVidia has conceded that they didn’t use stdcall, however, they said it wasn’t really a mistake because Khronos made the decision to use stdcall at a later time.
They have said that their next release will use stdcall. Sadly they didn’t comment on the exported symbol naming problem. So at this point I cannot be sure that their next release will be fully ‘correct’ and fully compatible with AMD’s SDK on a binary level. I think nVidia will do the right thing though.
There was no actual reply from Khronos itself on the matter though. So it looks like this problem was mainly solved between AMD, nVidia and some developers (I was neither the first nor the only one who noticed something strange between the SDKs and pointed it out on the developer forums, so I won’t take full credit) who were using OpenCL and who pointed them into the right direction.
On a related note, AMD has also released a beta driver with GPU acceleration for OpenCL, for both the HD4000 and the HD5000 series.