I found this after a fair amount of digging...
"Yeah, the dl part means that it’s an automatic download url, which means the link automatically makes you download the file/folder"
@CaptainMoto got me on doing this when I was posting frequently in the VJR. Do you remember why Moto?
I thought it gave the person attempting to view the Dropbox link a more direct path to viewing the link, without being hassled with the appearance that they have to join Dropbox to view the file (which is not the case either way). I don't think it is the end of the world either way, "dl" just provides a more simple viewing path with less Dropbox recruiting efforts directed at the would be viewer, and gives a different graphic view of the file being played.
I believe that was the long way to say that it doesn't really matter. Also if you go to Dropbox QA it looks like they are very busy changing things all the time.
It looks like you can also add "dl-0" or "DL-1" to the end of the link, another mystery to ponder.
Oh the wonders of the internet huh? you can find a reason for everything, may or may not be the correct reason though