It would be nice to merge all the duplicate postings for allowing compare dates in all reports. It would have a higher promote score then, no?

I can't agree more. Any report that can be generated for one date range should support the compare date ranges feature. It would be nice if it defaulted to the same number of days/months/hours when you opened the compare as well, but still be overrideable. I agree that this compare should stick as you navigate reports as well, just as single date ranges do today.