If this would be true only a handful of companies would specialize on them but anybody does. Cell phones for example are embedded systems and every man and his dog has a cell phone nowadays. If that's a niche market then I'm Santa Clause
Major players in the computer market ( HP, Acer and so forth ) sell netbooks. They would not if this would be a niche market.
NDS and PSP as the most sold handhelds ( even more than palmtops or PDAs how they are called correctly ). There are again major players ( HP and company ) in the PDA market so that's definitely no niche market.
The only point you got right in this post... you need to improve