This is why I hate talking to sales people in brick-and-mortar stores. Appearing confident rather than actually being correct is probably good for closing sales and for short-term customer happiness, but it's no good for the longer-term (ie, when you get home and realize you made the wrong choice).
Well, that depends--and that's where my metaphor breaks down. The customers went home satisfied and remained satisfied (at least, that's what their consistent repeat business and smiling faces would suggest).
Tomatoes and website loading times matter to you in the here and now but don't have any lasting effect on your life. That's not the case for making a major purchase.
You can apply the same reasoning to this UI element. Sometimes - most of the time? - the user doesn't really care about the amount of progress made. They just need to know that something is happening. But at other times, they need to know how much time is actually left on the progress. If that's the case, you need to care about more than just perception.