I do have it on good authority that sharp-shinned hawks do have sharp ridges that run the length of their leg bones.
These curiosities come to mind because yesterday, on the local Christmas Bird Count, Shearwater and I found six pied-billed grebes. None had noticeable spots on their bills because in their winter non-breeding plumage the spots are negligible, which reminded me of other birding caveats: immature red-tailed hawks have brown tails; female and juvenile ruby-throated hummingbirds have white throats; for the first two years, bald eagles have brown heads; and female black-throated blue warblers have olive throats.
To paraphrase the Bard: So what's in a name? That which we call a pied-bill by any other name would still be a pied to me.