I believe that any webdesigner, worth his salt, who intends to make sites for commercial organisations, should be well versed in W3C's accessibility guidelines. As a professional ability rather than a way of 'simply' complying with law.
I'd agree with KenB's statement,"A good bit of this thread sounds like it was written by professional activists rather than professional webmasters".
I have no problem with anyone who wants to make a site and put it online. I do get a little edgy when I see badly made professional sites, which could easily have their failings rectified with very little extra knowledge, apparently made by professionals.
I look at alt atributes as being a standard item to include in any website, along with many other items.
As to wether Target should be taken to task? Well yes, they appear to have ignored basic access guidelines and failed to correct this when notified.
I have no problem with that.
It would create a shambles if legislation was needed to ensure code standards on the internet.
Let's work harder at making it unnessesary!