My 2 cents...
For the GTD purists, the GTD Workflow Processing diagram suggests that for an actionable task, you should Do It (if the action will take less than 2 minutes), Delegate It (i.e. put it on your Waiting For list), defer it to a date/time specific item on your calendar, or put it on one of your "as soon as possible" next action lists (i.e. a context list like @Home, @Office, @Phone, etc.). So the methodology suggests that the act of delegating results in something on your Waiting For list. Accordingly, it would appear that (true to form), TR is following the methodology correctly by setting the status to Delegated. IMHO, the easiest workaround would be to use the Delegated status and put the task on a context list called "Waiting For".
However, for the non-purists, and in my experience using GTD (including several other TR-like tools), I agree with the need for a "Waiting For" status. I agree with the initial points made by douglgm concerning the distinction between Delegated and Waiting For. I too use Delegated where ownership is transferred and Waiting For for actions I still own but am waiting for an external event. As an example, I had a task on my "Phone" context to call a third party about a particular issue. I thought that I could close the task with a single phone call (hence not a project). Upon calling the third party, it became clear that they will need to send me something via snail mail to close this task. I don't want to close the initial task on my Phone context since the issue is not resolved. True, I could close the task on the "Phone" context and open a new one as delegated to the third party indicating that I am waiting for the material to arrive. IMHO, I think it would be better to simply change the status of the original task on my Phone context to "Waiting For".
I tend to use "delegated", when I'm dealing with people that I interact with routinely. I usually have specific @Agenda contexts for each of the people I interact with regularly. This allows me to Delegate tasks to them and I can see all of there actions on one specific context list.
claire to answer your question, I think there should be the option of a due date on the waiting for status. At a minimum, there should be a tickler date (follow-up date) to remind me that I'm still waiting for this particular task.
Again, the work-around could be to create a context called Waiting For and simply change the context of the original task. In my example above, I would change the context from Phone to Waiting For. But I think it would be cleaner to have a Waiting For status.