I too bought an ultrabook recently. Yet laptops are clearly decreasing year over year.
PCs are still indispensable tools. The problem is that the motivation to upgrade is not as it has been in the past.
There are a couple of reasons in my mind. The first is that tablets provide a better value to many that already have a laptop. They're more portable and convenient for content consumption. The choice in a world where discretionary dollars are limited, are to buy a laptop as an upgrade or a tablet/smartphone to fulfill a computing need. Think about the value proposition. The new laptop is faster and lighter, but most of my programs will not run perceptibly better. The tablet offers a new use case where mobility allows me to use a computer in many more contexts vs. a laptop.
Perhaps convertibles can solve the problem, but pricing seems to be a stumbling block there.
The second reason is that single thread performance improvement are at stall speeds. People will wait longer for larger improvements.
Perhaps a more controversial factor is that client PC computing is 'good enough' and has been for many years now.
An analogy is that PCs are like refrigerators. It's absolutely required to have one, but the replacement cycle is long.
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