Ask HN: Why are some people so sloppy with units?

So many times I see people sloppily use units incorrectly (e.g. kb, kB, Mb, MB) and I have to assume what they meant. I can't count the number of times I have had to ask if they meant megabit versus megabyte.

I have to assume it's either laziness (okay, maybe not), or maybe just a lack of understanding that capitalization is important. I still don't know what a mb is, although wolfram alpha happily corrects it to Mb.