Fern couldn't take her eyes off the tiny pig. "Oh," she whispered. "Oh, look at him! He's absolutely perfect."The adverbs of manner give the spice and emotion to this writing. Fern's attitude toward the pig Wilbur, (absolutely perfect), her loving care of the pig (carefully), the delicious irony of "heavily" armed. The adjectives are also essential here, tiny, wooden, perfect. White's writing is not any worse for not following his own lumpheaded strictures. Nor is this a matter of a "rule" that you have to be an expert, already, to break. You cannot even begin to write well if you deprive yourself of an important tool. This short passage also contains three forms of the verb "to be."
She closed the carton carefully. First she kissed her father, then she kissed her mother. Then she opened the lid again, lifted the pig out, and held it against her cheek. At this moment her brother Avery came into the room. Avery was ten. He was heavily armed -- an air rifle in one hand, a wooden dagger in the other.
I guess you could ruin the passage by adding a few more adverbs of manner. "she tenderly kissed her father..." But so what? Nobody has ever made the opposite claim, that where adverbs are concerned, the more the merrier.