Nope. They're the same stuff designated for different areas. WM-11 are the units designated for export to Canada and the US while the rest of the world got the WM-22 model. US units have and additional star icon on them, while Canadian units have a maple leaf one. It would be interesting to find out why Sony did this to some units and not others. Another unit getting same graphic treatment is the WM-F8, while different model numbers between regions are quite common, especially in the case of Japan and export models.
It probably depends on their intended pricing and Guarantee period (which would always be one year in the UK) I was going to say that it wouldn't happen on a high end unit, when I remembered the ICF2001D/ ICF2010 radios, which are the same apart from the number. Canon and Olympus seem to use all sorts of model names and numbers for the same Cameras I have even seen exclusive to Currys models wich presumably allows them to sell them cheap while not upsetting companies like John Lewis' "Never Undersold" policy.
That seems to be a good reason. It'd probably make things more organized on Sony's side of sales & support. I'm still wondering about the star & maple leaf icons though. There were a lot of walkman models from the same period, but only a few models were given the icons. Well, in any case, I think like they look better without the logo... Perhaps that's part of the reason.
