>The point is that these middleware appliances we often use as a scapegoat exist only in well-controlled private networks. Why should we care about them?

Perhaps for the same reason we only stopped caring about IE 6 after its usage dropped below a tiny percentage.

For better or worse, making your website available to as many groups of people as possible, regardless of their browser selection or network configuration, has been a long-standing goal in the community.

If your website isn't available to folks at the offices of company X because they use appliance Y, through no fault of user Z's, well...that's not ideal, is it?