You are correct that progress is evaluated strictly by the status of the task. The reasoning behind this decision is the notion that Done is the value that matters, as any estimate on remaining work is just that: an estimate. In practice the values indicated in remaining work fields are often inaccurate, either because they are not entered, out of date, or simply very difficult to guage. Many of the members of our team have witnessed on past projects the classic "90% Complete" phenomenon where a task is reported as being 90% complete but takes ages to ever reach 100%.
Furthermore, from a product completion standpoint, a task that is 90% complete is just as useful as a task that is 0% complete; that is to say, neither are useful at all. A task that can be useful at 90% completion likely could have been decomposed into smaller tasks, and the indication of Done on those tasks would allow for a more visible and accurate measure of completed work.
Down the road we do plan to include a field for tracking actual time spent on a task, which we can then use to drive further analytical estimation techniques. This could then be used in conjunction with the estimate field to derive remaining work for those that wish to do so.
the Telerik team
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system and vote to affect the priority of the items