W221 S500 and S550

The German version of 5,5-litre V8 motor is called S500, SL500, and GL500 whilst the American version is S550, SL550, and GL550.
What is the reason for retaining 500 designation for new motor? Does that have to do with Ferrari 550 Maranello (superseded by 575 Maranello)?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.