Nonsense. They never grounded the worldwide fleet of 747s, but they most certainly "attempted to look at or fix all of the other planes." (link).
The FAA does not believe detailed in-tank inspections of the FQIS components would be effective because the condition of in-tank component or wiring contamination and damage can be difficult to detect while the parts are installed. The agency believes the best approach at this time is to replace the current in-tank FQIS components with new parts, including replacement of silver-plated copper wires with nickel-plated wires.
The FAA is proposing that operators remove and replace FQIS components within 20 years from the date the airplane was manufactured, or within 24 months of publication of the final rule, whichever is later. Nickel-plated wire is much more resistant to corrosion in the presence of sulfur.
That's a rule change. It specifically says that an inspection would be impractical. They didn't look at the planes. They just changed the rules for maintenance.