In a single-level loop, i is just an offset. I agree that depending on the context (maybe even for the vast majority of for loops like you're suggesting) it's probably fine.

But once you nest three deep (as in the example that kicked off this thread), you're defining a coordinate space. Even in a 10-line block, i, j, k forces the reader to manually map those letters back to their axes. If I see grid[j][i][k], is that a bug or a deliberate transposition? I shouldn't have to look at the for clause to find out.