I stand behind this decision.
First lets look at the definition for unsung hero:
a person who makes a substantive yet unrecognized contribution; a person whose bravery is unknown or unacknowledged
from dictionary.com
I agree that Jon / Marc and Eric may make substantive unrecognized contributions at times, but their "bravery" is very acknowledged. They should not be getting this badge.
If you think there needs to be particular tweaks to this badge, post separate requests, with backing data, one per request. Some reasonable ones I heard are giving it out retrospectively, or changing zero score to zero votes. But before doing this I need to look at backing data.
If you think there needs to be a new badge that acknowledges participation in obscure tags, I'm totally for it, but this should be a new badge that we need to think out. Post a separate meta proposal on it.
The concept here is encourage a behavior that is not normally encouraged using our reputation system. It is not meant to be a badge that is easily achievable nor is it meant to be a badge that everybody wants to get.
The concept here is to give these "poor users" that participate in tags that are not wildly followed or upvoted or happen to answer less popular questions some extra incentive to keep on making Stack Overflow better.
Take david kanarekdavid kanarek for example, he posts lots of answers in the iPhone tag, for example this onethis one, a correct technical answer for a complex iPhone issue. The thing is, for some reason people do not upvote this stuff. Perhaps the iPhone crowd did not discover upvote button, perhaps its the low views, who knows. What we do know is that we want David to keep on contributing to Stack Overflow, so we give him a badge for his efforts.
This is not meant to be another badge amongst the 1400 badges Jon Skeet already has, its about giving these users that contribute in a less popular way an incentive to keep contributing.