There are industry standard specifications for engine oils, gear oils, hydraulic oils, turbine oils, etc. Standardized specifications are wonderful for the end user, simplifying product choice and ensuring a certain level of performance. This also facilitates cross-referencing, and ultimately, a degree of product commoditization.
Greases are different. There have been very few industry standard specifications, and as a result no two greases are exactly alike. Grease performance can vary not just due to formulation differences, but also as a result of the manufacturing equipment and processing used. The wide variety of grease applications creates a need for product differentiation, but makes it difficult to compare performance of the many greases in the marketplace.