chill there, raz, we've all been here for many years.
if you want my background, I grew up in Southern California, went to university in the bay area, and am now working/grad school here in New York, so what I speak of are from first hand experience. You will occasionally hear people use the term 'townhouse' and 'rowhouse' here in NY, and I'm sure all of them are interchangeable, but for the pictures posted in this thread, I can assure you that most people here would call them brownstones. I wouldn't necessarily call them mutually exclusive. In modern connotations, the term 'townhouse' is best described in the following:
The name "townhouse" or "townhomes" was later used to describe non-uniform units in suburban areas that are designed to mimic detached or semi-detached homes. The distinction between dwellings called just "apartments" or "condos" is that these townhouses usually consist of multiple families, usually multiple floors. The traditional "townhouse" apartment is a two bedroom unit with the living room in the front on the lower level, kitchen in the back. Two bedrooms are on the front and back of the upper level with a single bathroom between. This style has become less popular in areas where it has been adopted by rent control or HUD apartments.
in otherwords, the suburban townhomes usually exists in affluent suburbs where land still costs a premium (and thus many people still choose to live in conjoined townhomes rather than individual residences). check the following pictures for examples: http://en.wikipedia.org/wiki/File:Tracthousing.jpg
and this of course was popularized in California.
As for the east coast, every once in awhile, you will here the word 'townhouse' used to describe very large condos in an attempt to glorify it at a level above regular single story condos. These can be located in brownstones, rowhouses, etc.
and i think anyiliang was agreeing with my comment about taiwanese response to american english, not housing definitions