You can't argue about market share, since it's minuscule. If you want your websites to run on _all_ mobile devices, you'll also need to support Opera Mini, Symbian's built-in browser and whatever else is out there. Those latter two have way more installs than there are win phones, by the way.
You can't argue about corporate users being forced to use IEMobile. It's a person's _choice_ to use a windows phone, and Microsoft's responsibility to make it a pleasant experience, not yours.
You can't argue about market share, since it's minuscule. If you want your websites to run on _all_ mobile devices, you'll also need to support Opera Mini, Symbian's built-in browser and whatever else is out there. Those latter two have way more installs than there are win phones, by the way.
You can't argue about corporate users being forced to use IEMobile. It's a person's _choice_ to use a windows phone, and Microsoft's responsibility to make it a pleasant experience, not yours.