Plenty of mis-information in this thread.
This is about a clueless person speculating. Canon did release updates for that camera later, and all 70Ds are eligible for upgrade.
SN check: they want to prevent people from unnecessarily trying an update (an update that would not apply because the cam in question already has the same or newer fw version).
I can't recall any models that need different fw updates depending on their serial number. So, if they happen to change a hw component in a model during production (not sure if that ever happened), newer versions of the firmware would still be made compatible with old hw revisions. Not doing so would be a nightmare in case they are forced to fix, say, a security issue.