Of course, this is completely backwards. The rating system had nothing to do with arrow spine, directly anyway, and the numbering system wasn't necessarily sequential. And Easton's competitors don't want to be seen as "copycatting" Easton by following Easton's sizing format. Never assume an arrow's published spine size matches the arrow's actual deflection. If you go by the simple chart method, then you'll need to apply a little common sense - particularly if your bow setup isn't exactly 'average'.
Since carbon arrows had a much broader ranger of application, there was no need for 10 to 15 sizes of the same arrow.
For Recurve/Compound Bows
To understand the issue of arrow spine deflections and why they aren't just standardized, like tire sizes or plumbing fixtures, you must understand something about the history of the arrow industry. It's still the Wild West in our little niche market and everybody wants to be the new sheriff in town. Okay, it wasn't so easy. To be fair, Gold Tip's system really wasn't so bad, comparatively anyway. So why mess with tradition? As long as the various carbon arrow manufacturers provide their spine deflection data and they test using the industry standard methodmanufacturers can size and market their arrows by any system they like, and we can still reference the proper application from the gold standard Easton charts using actual spine deflections. The rating system had nothing to do with arrow spine, directly anyway, and the numbering system wasn't necessarily sequential.