Actually it isn't. Still going as strong as ever. Especially in the Government & private sector medical & office sectors. Desktops will never go away. Only thing that will change is the way we will interact with them, along with the software, but the beige box market will never die.
Only reason that most consumers are going with Smartphones, is because they are cheaper now, than they were two to three years ago. As for tablets, the market share is not as big as you think that it is. Even with the price range that it is, there are still a lot that are either not going to adopt the tablet interface yet, or are still confused, because there are too many brands out there.
The numbers are just not there, in showing that there has been a huge consumer demand for portable devices as you are thinking, in the way of tablets & laptops. Even though using smartphones, do not use the full power that they offer. Most just text, take photos to share on facebook, or make calls. There is more to a smartphone, than those few items, that you can do.