Question o "Easy Freestyle" by Terry

[wie]

From the TI-easy-freestyle-manual.pdf page 5:

In 1992, USA Swimming researchers Jane Cappaert and John Troup found that elite swimmers at the Olympics generated no more stroking power than average swimmers. Cappaert and Troup concluded that their superior speed resulted from 'better whole-body streamlining.'

I wonder if this is correct.
Why then are elite swimmers so muscular and do so much muscle training?
Is this just for better streamlining?