Ozzie
Hm, i manage plugins of c4d in visual studio, between x86(win32) and 64-bit(mostly it's easy to switch x86 to x64, click to which build need to compile)...but stack if used new additional libs(like intel embree) which will handle normally at x64(need more RAM)
currently Maxon dropped win32 or x86 platform...
I think why not x64:
1. management of security options as licensing
2. several plugi-ns which used or mentioned by Ian as used technology are x86 platform based
example - sketchup reader, but new x64 reader appeared in latest sdk from Trimble
(i'm sorry for my English)