The sRGB black point just means that (0,0,0) is assumed to have a luminance of 0.2 cd/m^2, because your screen reflects ambient light and other factors.

Ignoring it will give you nonsensical values when you try to do conversions into other color spaces or when you try to do color comparisons.

Source?

As far as I can tell in XYZ black is (0,0,0) and the only sRGB value that maps to that is (0,0,0)

This is incorrect.

If sRGB (1,1,1) is XYZ (1,1,1), then sRGB (0,0,0) is XYZ (0.0025,0.0025,0.0025).

Or if you are using absolute XYZ values, sRGB (0,0,0) is XYZ (0.1901,0.2,0.2178).