I found this a strange decision in the Grid standard design. Surely most people* would think more in terms of "cells" that "cell-dividing-lines". Then again, compared to the design decisions in much of the rest of CSS including every other standard layout mechanism this is a fairly small gripe, overall CSS Grid is a big improvement. And when using the excellent "grid-template-areas" (compared to ASCII art elsewhere in this thread) you don't really specify start and end points anyway.

* By people, I mean designers (used to bootstrap-style grids), coders (used to arrays) and everyone else (used to spreadsheets).