Exactly... People who are being ignored usually have reason to be. If you're too dim to realize I'm just busy, then I probably don't want to be texting you anyway. If you're in a situation where I might be ignoring you because you did something to perturb me, I'd rather you assume I'm ignoring you, because then it'll drive the point home.
In practice, however, I find people can usually tell via context that they're being ignored. There are some subjects you'd expect this or see it coming before other, more benign ones.