Since ActiveSync is a patented and licensed technology, no major manufacturer is going to make a device that falsely claims to support remote wiping but actually ignores the command.

Remote wipe is usually implemented by simply re-setting the hardware encryption key, so there's no easy way to have remote wipe destroy only the corporate data.

http://technet.microsoft.com/en-us/library/bb124591.aspx says that would actually be acceptable, but they note no manufacturers have created devices that are capable of selectively wiping only corporate data.