Hans Aberg
7. Juli 2015 10:30
On 7 Jul 2015, at 04:46, Wolfgang Schuster <schuster.wolfgang@gmail.com> wrote:

The spacing is different in cases - TeX also has such a variation. Specifically, there is extra space before the conditionals.

In addition, it seems \startmathcases ... \stopmathcases is not working with UTF-8: in the example below, the ω’s on the second line, after the arrows, disappear in my PDF. 
This is explained in section 8 of the document:

FYI, the TeX Live 2015 version from 2007 called context-latex-math.pdf does not have ch. 8.

    There are two ways of specifying the second column — \MC (Math Column)
    and \NC (New Column). If \MC is used, the second column is in \math mode,
    with \NC it is in ‘text mode’.

I get errors when using \MC - see example below.
The \NR before \stopmathcases is missing in all your examples.
But the spacing is wrong: too much between the two components. These are not cases, but aligned formulas: one might have a number of alignments, not just one. And I just happen to use left braces on them.

Take a look at my previous example where I changed the distance between both columns with the distance key.