So basically it makes the the WoW64 version of Wine backwards compatible with the pure 32bit version of Wine, in addition to the pure 64bit version of Wine.
Note that the WoW64 version of wine realy is two separate applications, a pure 32bit wine binary and a pure 64bit wine binary, but with some extra glue code to hand over windows executables in the wrong format to the other one.
This is actually quite similar to how the 32bit wine binary doesn't know how to handle 16bit windows applications, but hands them over to the winevdm binary that does. The main difference is that winevdm on the linux side is a 32bit binary that uses 32bit system libraries, so you don't need any special 16bit linux libraries, while WoW64 wine uses the regular 32bit wine for 32bit applications. I guess it would be possible to do something similar for 32bit windows applications on a 64bit linux, but that would require some massive reengineering effort, so is unlikely to happen anytime soon, if ever.