I guess the difference in "ground" and "air" limitation exists because in the air fuel is cooler than on the ground, so running the CTR pumps with less than 453 Kgs in flight is not as dangerous as running them on the ground.
Kinda interesting, the 453kgs limitation is only found in the the cockpit preparation part of our manual, it is not listed in the limitations part.
The "Limitations" section of the FCOM 1 doesn't contain limitations that are found in the other sections of the FCOM (such as Limitations contained in the Normal procedures, Systems sections and so on).