Ok, that makes the current expected behaviour clear. I'll manually add in the vcredist to my package and fill out the install instructions field.
FWIW I like the idea about automatically including prerequisites and generating a description for the install instructions field. I can't see a way of integrating prerequisites with just a zip download so automatic handling would be the next best thing from my perspective.
EDIT:
Haha looks like the 'install instructions' has specific language in the description indicating that steps for installing prerequisites should be included there, guess I missed that :P