Ah, sorry, did quite get you there. Why did you want it in the SF's download system (apart from getting to use the Mirrors)?
Not me want it
, but SF projects do.
The main advantage is that this is the primary means of bringing attention to your project - your download stats are only tracked from the dl system, and that is converted into the primary component of your "activity stats", which then in turn are used to generate your SF rank.
Higher SF ranks push your project to the top of the SF search results, amongst other things, and generally lead to an increase in hits from SF surfers.
You also *only* get to see your daily/weekly/monthly hits graphs based on downloads from the system (although page-views are counted too, it's the downloads that seem to really matter).