He said "Seven- to 17-inches is our sweet spot" since screens of smart phones and other small mobile devices are too small to make a good multitouch interface.
My opinion is a little different. First, Apple iPhone anyway has shown an excellent way of applying multitouch to small screen devices. Second, I think that N-trig's DuoSense is much more important feature than multi-touch. With DuoSense technology, a user can use pen and multi-touch simultaneously. Pen input is very important feature for Chinese users due to their complex character system (ideogram).
So, I slightly modified N-trig's opinion: 1) seven- to 17-inches is a sweet spot of multi-touch and 2) cell-phones and smart phones are a sweet spot for DuoSense.