I agree , there are other reasons to use PPC even if you have great organic rankings:
Time sensitive offers ,
Horribly misspelled words (one word can have hundreds of misspellings or typos)
The ability to show up on the content network
A/B testing for conversions
Targetting a specific geographic area even if your site is geolocated elsewhere
Keyword research - broad match can give you all sorts of interesting data