(@wkeese: when I started to work I used what is on D1 dijit and dojox/mobile, that is why started to work with indeterminate).
Reasons why I kept it:
- you can not set a value to infinity when you declare a widget in pure HTML. 
- As a user it is convenient to have a simple flag. The widget has 2 possible states; determinate and indeterminate. This is intuitive a have a flag in such case. The relationship between the flag and the value is consistent as well.

Now if we want to remove it I have no problem with that. I just say it is simple to use and it works.