That wouldn't cut it for me, since I don't feel it is a reasonable mistake for support staff to be making. If you are hiring people to process RMAs, and they don't know what an operating system is, then I obviously can't put any faith in your RMA process. If its just "we hire clueless people and don't care" then all sorts of other legit RMAs can be rejected too. I don't have the time nor inclination to fight with a company over crap like that, so I just stick to ones where I know I don't have to.
It would appear that it was not a mistake. This is precisely why I need to hear a very clear "we messed up and are taking action to prevent it from happening again" rather than just "oops".
That, to me, is what seems like the reasonable respond from Newegg, but I don't think anyone would want to hear that.