Explanation of what higher costs buy with Grado

Can anyone give an in depth explanation of what one gets with increasing costs in the Grado woodies? Their website is remarkably vague. The only differences between the Sonata, Master 1, and Reference 1 listed on their website is an elliptical stylus in the Sonata & Master 1 vs. an ellipsoid stylus in the Reference 1. With the steep slope of the price increases between these three models, one would think that there has to me more than a difference in stylus profile.
Typically the higher models are the cartidges that measure the best. In otherwords, the cartidges are made then tested. The cartridges that measure good are the expensive models and the cartridges that don't measure good become the cheap models. They measure for frequency response, balance, separation etc.
I assumed that some of the factors you mention are involved. Soundsmith, for instance, is very upfront about this. However, they also have factors of cantilever material and stylus shape entering into their increasing prices. Same holds true for the increasing prices through Ortofon's range of 2M cartridges. Different plastics & resins in the bodies as well as stylus profile account for increasing price. It seems unusual that there wouldn't be any more to Grado's increasing prices than tighter tolerances to account for a near tripling of price (and a stylus profile change in the Reference.)