We're hesitant to add this particular option. There's some fairly major problems with either choosing 'Yes' or 'No' , in that if someone chooses 'No' they may in the future forget that they checked off the 'Always Use This Answer' and become frustrated when clicking 'download' does nothing. I know this happened to me at one point when I was testing the addition and had forgotten what my particular options were. Likewise, if someone chooses 'Yes' then it's a fairly large waste of network resources to continue downloading something you already have.

Checks for other shared folders are possible in the future, as well as checks for the hash/fingerprint of the file instead of just the filename.