Well, I would treat the 10-inch displays of tablets as a replacement to many PC displays to begin with. It is true that sales of larger screen montiors are declining but one could argue that the gains made in 10-inch display in tablets have more than offset this decline.
I think its combined smartphone and tablet segment that is eating out the desktop and it is reasonable to think so because those who own a laptop at office will not go for another one at home. Rather they will opt for tablet which they can carry around without much problem.
Even the mid sized LCD's such as 15 inch to 19 inch might slowly disappear from the consumer market considering the fact that less than 10 inch are coming into tablets and more than 21 will be more used for desktop displays.