I have most, if not all, of the old oggenc2 sources available if really needed. There about 10 previous versions.
As stated by HotshotGG, some of the differences are that it will accept input from most of the lossless formats although FLAC integration is the cleanest as it uses the same routines as the standard oggenc. For FLAC input, the option also exists to 'scale' the input using the vorbisgain tag info from the FLAC files. There is also the option to pad the headers for adding subsequent tagging info without the need to rewrite the files but this requires the support of the tagging software to work effectively.
Other principal differences are that it includes third party provided unicode patches and probably most significantly, it provides correct support for multichannel file input in line with the vorbis I spec.
How many of these changes are portable, I have no idea, I am a 'linux virgin'!!

I'll provide any assistance I can, within the limits of my knowledge, and we'll be more than happy to host a successful project at Rarewares.