I'm just getting into this myself, but I've picked up on a couple items in my searching. Correct me if I'm wrong ...
I think the gribs that come down from zygrib are very reduced because the sailmail is limited to very small files. Otherwise, they would contain much more info ... since some of NOAA's stuff actually is BOM AFAIK...
The original NOAA grib2 files and BOM files are often very large in size, like even 100MB, which is a significant little chunk even for some
wifi connections. The NOAA no longer distributes the original (smaller) grib1 files. So, some kind of conversion and reduction is needed for sailmail. I think zYgrib does this, but am not sure. Naturally, there will be a ton of additional info in the bigger original grib2 files. If you want to analyze the latter, I've come across some good programs for doing it: CDO (Climate Data), which is available in an installer package for various platforms, gRaDs, a similar program, and various R-cran (statistics) programs if you're familiar with that system.
Like I said, I'm just getting my toes wet here, so feel free to add your own knowledge, or correct it ...