Drupal versus with Omni Update: Should I move from Drupal to Omni Update? Use Case


Current (aging) IT website built on Drupal 5. 
Most people hate this website because the theme is awful and adding content is painful.
An upgrade to Drupal 6 and a theme / module updates are what are needed. (Not considering Drupal 7 until more modules are available.)
Some of our leadership thinks we need to switch platforms anyway.


Argument


What are the pros of sticking with Drupal versus switching to Omni Update?
What are some pro Drupal buzzwords that nontechnical manager-folk will understand?
What is your best argument for selling Drupal to a prospective client?
I think you might have answered your own question: "it will turn into a LOT of work if they decide to switch to the proprietary platform". Work = time = money, and that is manager-speak.