Older viewers will remember that originally, contestants were not given these letters automatically at the start of the
final puzzle. They were asked to provide five
consonants and one
vowel. As the show became more popular, the best
strategy seemed to be to select those six letters, and it was rare for someone to pick different letters.
Sensing the banality of the final puzzle, the producers decided to change the final puzzle format, supplying the contestants with these six letters, and asking them to provide three more consonants and one additional vowel. You'll notice now that although the majority of players pick 'CDM A', those who choose something different, like an 'h', a 'p', or an 'i', far outnumber those who strayed from the old standby of 'RSTLN E'.