[manarth]

  It's an accessibility thing. If I designed a new web system that
  blocked off 10% of the populous, for whatever reason (deaf,blind,
  not able bodied), then people would call me out on it.

Rightly so, because that's a constraint that cannot be changed.

Running an outdated, decommissioned operating system is something that can be changed. You have no obligation, moral or otherwise, to support Windows 3.1, OS2/Warp, WAP browsers, Gopher clients, or IE5 running on Mac OS 9.

You can still choose to support outdated clients, because it makes financial sense for your organisation - and many places to just that - just as a corporation running outdated software may choose not to update because that's what makes financial sense for them.

Equating support for an accessible service with support for outdated browsers is a non-starter.