Executive summary: "There should be a tool" (sorry, I'm not volunteering any time soon) that could be added to $VCS diff (say, "git coverage-diff" or "git diff --coverage"). Chris Withers writes:
It's an interesting point; I personally don't see much value in coverage of less than 100%, if you're going to look at coverage: no-one is going to focus on or potentially even notice whether coverage moved from 99% to 99% (no typo), even though a bunch of new uncovered code may have been introduced.
I agree with the point you're making (that the difference between 100% and 99% is a very significant indicator that "something needs to be done here, it's obvious what, and [depending on project process] it's obvious who, too"), but it's also true that 99% is better than 98% and definitely better than 90% or less. Your point that it matters *which* 1% is more important, I think (see "Executive summary").
If people are actually using these blocks, then so be it, but it feels like the people who want them to stick around are saying they're using them just on the off chance they might use them, which feels like a poor reason to keep a bunch of dead code around.
At least one person says he uses it, although I don't know how that fits with Robert's statement that "it was never needed". Steve