For creators, PCs are indispensable. Like you, I couldn't fathom using an iPad to write code or prose.
However, consumers don't need the creative powers and capabilities of a PC. In this paradigm, phones and tablets are a simpler, more portable consumption terminal.
Creators, both business and otherwise, will need machines that let them design, code, write, and analyze. Consumers never needed these capabilities, and now that there are compelling devices that offer an arguably superior media consumption experience, creation machines will be put on the margin.
A significant minority of non-professional users of computing devices are consumers, rather than creators of content. But the defection of this significant minority is enough to impact the bottom line of companies like Intel.
This server would provide all the horsepower, centralized storage, and session management (think IRC chat etc) that you need -- and you can access it on any device in your house.
Imagine a keyboard running a tiny OS that could detect the nearest registered display. You could write code on the TV for a few hours, walk over to a desk and pick up where you left off. That's what I would eventually like to turn my home into (by setting up a Plan 9 network and writing terminal clients for android set-top boxes), but it's hard to find the perfect home server.
Power users (developers, designers, etc) are such a small fraction of overall users we might as well be 0%.
I'm excited about Haswell, but only because it's supposed to come in under 10W. I feel like MBA battery life took a step back with Sandy Bridge/Ivy Bridge (the mid-2010 model lasts forever on a charge).
And they have been, losing sales first to consoles and then to smartphones and tablets. Children are growing up on Xboxes and iPads, not PCs.
Desktop PCs will be like pickup trucks, to reference Steve Jobs's famous analogy. Someone will always need them, but most people won't have them.
The day that providers start releasing tablets with 1TB of storage and ability to add-on additional storage with ease is the day a tablet can compete with a computer. We live in the day and age of extreme data consumption, tablets with their minuscule 64gb of storage aren't enough to store the modern day PC users information. Cloud storage might eventually fill that gap one day, but the Internet even in some of the most developed countries is still unbelievably behind and bandwidth still expensive (and I would know, I live in Australia and people in New Zealand pay even more for less) not to mention cloud storage as proven by Amazon's constant downtime isn't reliable enough to store information that is guaranteed to be accessible all of the time nor can you access cloud data without an Internet connection and wireless Internet connection options like 3G or 4G are very expensive for so little in data allowances.