The different "row end" commands make a better spacing. Better use <cmd>SR</cmd>, <cmd>FR</cmd>, <cmd>MR</cmd>, <cmd>LR</cmd> instead of <cmd>NR</cmd>. You can also use <cmd>AR</cmd> instead of <cmd>SR</cmd>, <cmd>FR</cmd>, <cmd>MR</cmd> and <cmd>LR</cmd> (AR for automatic row).
If you need information about <cmd>placetable</cmd> look after <cmd>placefloat</cmd> in the manual!
This mode is based on Michael Wichura's TaBlE package for PlainTeX. The official manual for it is commercial (about 40 USD), see [http://www.pctex.com PCTeX] -- but note that the TaBlE manual only talks about the original syntax, which does not use <cmd>NC</cmd>, <cmd>HL</cmd> cum suis.
The only ConTeXt docs about it are in [http://www.pragma-ade.com/general/manuals/ms-cb-en.pdf ms-cb-en.pdf].
The sample looks like this: