In the case of wl, it is probably simply a matter of newer is better.
I am aware of
wl0: Mar 4 2010 00:00:47 version 126.96.36.199
In the case of BusyBox, I am aware of three levels:
1. The version of BusyBox.
2. The commands that are included in the Config file.
3. The functionality that is specified for each command in the Config file.
 I am aware of BusyBox v1.18.5. For the most part, newer versions mean better bug fixes. For example, sort may be very broken, somewhat broken, or working properly. I have enabled some bug fixes, including an awk bug.
 For example, a distro may include string but not arping.
As a sysadmin, on a router, I would much rather have arping than strings, especially since the functionality of strings is easily implemented in 150 bytes.
 This is not very well known — even with the same version of BusyBox and the same set of includd commands, functionality can vary drastically. For example, the shell may or may not have job control. The nc command may or may not have "-l" (listen). Vi may or may not have undo and .exrc.