Manoj writes a bit about [appliances versus tools](http://www.golden-gryphon.com/blog/manoj/software/manoj.2004.06.17.golden_gryphon]. He’s saying what I’ve been trying to say about user interfaces for a long time: A bit simplified, you can divide the “cost” of using an UI into two parts: One initial cost, which is what it takes to learn the interfaces, and one running cost, which is how much it costs to use an interface after you’ve learnt it. Of course, this is a bit simplified, since learning a tool is not binary, but I still think the comparison holds.
For tools which you use seldom, you care a lot about the initial cost, since you will incur that many times as you have to re-learn the user interfaces. An example would be an ATM. For a complex tool, such as my use of a computer, the running cost is what matters. If I have to spend a week to learn a tool I’m going to use a lot, it’s worth it.
However, as Manoj points out, this is not only a result of complexity: Both ATMs and general purpose computers are complex beasts, and an axe is a lot simpler than a refrigerator (mechanically speaking). The HCI term “affordance” doesn’t quite cut it either, as it is more about how easy an interface is to learn. On the other hand, an axe affords a lot of things, that is, it doesn’t give you much guidance on how to use it. A refrigerator door affords opening, it’s one of the few things you can do with it.