It's not quite simple, but I think we are suffering from programmers who haven't adequately coped with the changes in the technology.
Computers used to get more powerful by running at a higher speed. That hit some practical barriers, and the response was the multiple-core processor. You get some gain just from the OS running on one core and the program running on another, and that's easy to do.
I can point to software, written in the last three years, able to use a lot of CPU power, which is still stuck at that crude level of multi-core use. Luckily, a lot of the work the program does can be handled by the graphics hardware, but the performance seems biased in favour of a particular GPU manufacturer.
Add the way that it grabs all the RAM it can, and that there is no 64-bit version (that might be an advantage, since it limits the RAM it can grab), and you have an indication of how programmers are failing to exploit the increased hardware speed.
And my fancy multi-core desktop monster doesn't really improve things for writing this comment. I don't type any faster. OK, so it has a bigger screen and a better keyboard than my netbook, but the feeble CPU isn't the limit on what I do.
We have too many programmers producing badly-implemented usage of processing power. I'd far rather see some smart exploitation of the falling energy costs. I used to run an office on a 1 GB hard drive, with plenty of storage space to spare. Now a memory storage device that small is becoming a little hard to find. But is the energy cost of storage reducing in a useful way when a similar physical device can store 2 TB. "Laptop" drives, of course. It does seem that cheap laptops are where people are spending their money, these days, and they are hugely powerful computing machines. They are saving energy, but they don't do so much more on a battery charge. We don't type any faster.
I don't mind having these huge hard drives. But Parkinson's Law seems to trump all else about computing. With a touch of the Peter Principle.