This is hilarious! I contacted Channellock about this and they said...
"Hello Rick -
Thank you for contacting us about the 369 linesman plier.
This plier is designed as per Klein's original linesman plier - the "step" has always been there, and if it serves a purpose, we do not know what it is, but it is an expected feature.
Sorry we did not have more information for you.
Have a nice day.
Channellock, Inc."

http://www.kleintools.com/content/history said:Perhaps the only job Mathias Klein ever did "halfway" involved the first tool he ever made, which was — in fact — one half pair of pliers. A broken side-cutting pliers was brought to his forge shop by a telegraph lineman. Mathias Klein forged and finished a new half for the tool, riveted it to the old, and the lineman went on his way. Shortly thereafter the lineman returned. The other original half of the tool had now broken and Mathias Klein forged the second pliers half, producing the first complete Klein pliers.
Hello, 1st post.
No idea about the coating but I'm pretty sure the nose is ground like that so it'll measure under 1/2" wide at the tip (and fit inside 1/2" conduit when used as a reamer.)
How did your other pair get donated? To someone elses tool box?
After I emailed Channellock and they said they didn't know what the step was for but they copied the Klein design, that wasn't good enough for me. I emailed Klein and sure enough they said their step was for reaming. Back to the round nose 369's... the tip geometry is .055" at C and .028" at F per their drawing.
Anyhow, I like them for what I bought them for, amateur electrical stuff.