When the reputation points were activated some months back, almost all posters had one green bar except the moderators due to their responsibilities of looking after the site. Some posters just happen to end up with a gray bar and were just likely missed by accident.
Since that time, reputation bars have been added to numerous posters for their contributions to the site. Has everyone been looked at to see their reputation level? Absolutely not! We have over 60,000 members it would take forever to review. We try our best from time to time to show our thanks to our posters by adding a reputation bar. Have we covered everyone equally? Not likely, but it is not by design as we appreciate all of our posters. Hope that helps a little.