I know these are your heuristics, but find it quite puzzling that you think the average web designer using ASP or Windows is an immediate rejection. What are you saying here?
There is a difference between a designer and a developer. If you are hiring for designers why do you care if they can program at all. I know dozens of designers who couldn't write a hello world in Python yet have a beautiful web portfolio and yes some of them use windows.
You mention web designers--out of the dozens of designers I respect, I don't know a single one who uses Windows. Do you?