Webster was an orderly-minded man who disapproved of a lot of the spelling that Johnson had recorded (indeed, he disapproved of a lot about Johnson, saying that he was ‘naturally indolent and seldom wrote until he was urged by want. Hence… he was compelled to prepare his manuscripts in haste.’).
Webster’s dislike of words that weren’t pronounced the way they looked led him to decree that words such as centre and theatre should be spelled center and theater; he also dropped the silent u from words such as colour, favour and honour. In fact, Webster was single-handedly responsible for most of the differences between British and American spelling that survive to this day.