That's the thing -- it's an entirely different ballgame on the ambiguity front when they've contacted you first (versus the other way around). In that case, at least presumably they've already mulled over the potential skill gap, and (again, at least presumably) saw something in you that significantly outweighs that gap.
OTOH, if they have a big sign on the front door that says "requires 5-8 years of X,Y,Z" -- in addition to all the other randomness one has to deal with when initiating contact (Will they ever respond? And will they ask me do some silly exercise requiring 5-20 hours before proceeding pass the initial contact?) -- then of course my answer is "Meh, I think I'll pass."
And if they genuinely expect candidates to be "bold" and second-guess their stated, bold-font "must-have" requirements, then they've definitely entrusted the wrong person to edit the final copy of their job reqs -- or they're playing (some really quite silly) head games with themselves.