Because it is the "official" Handbook. And that it is impossible to design a accurate character from the comics. Hero's strengths and abilities fluctuate wildly from writer to writer and year to year. So instead of holding on to a issue you read five years ago as a baseline for the "Things" strength it seems more logical to use what marvel has said is the official strength level. Even if they break thier own rules it is at least what they concieve the character's power level "should" be at.