That's the count of the number of .t files mentioning the package.

And Test::NoWarnings didn't make it in because while it's a great module, it's far too problematic to turn on by default. For example, we have over 6,000 individual tests being run with Test::Aggregate and Test::NoWarnings had to be disabled. In fact, my current version of Test::Aggregate (not uploaded as of this writing) has code which disables Test::NoWarnings on demand because of how it plays havoc with aggregated tests (and also makes checking the 'plan' very difficult).

Yes, Test::NoWarnings and plans has always been annoying. I remember thinking when I wrote it that there should be some way for a test module to declare its own plan that would independent of the script's, but that all ties in to the blocks/nested plans feature that TB might some day have.