Technically a "PC" is any consumer computer, so a Mac is one, but marketing has caused the term "PC User" to be associated with Windows. Call computers what you want, but they're still all the same in the end, right?
Paintings of Apples? I'd go for aluminum walls instead. The look of a person's face when you "pull a laptop out of the wall" would be priceless. Nice joke.
One person's junk is another's treasure, but still, most consumers do not understand what they are getting for the most part. For instance, people who walk into a Best Buy, or any consumer electronics store, may purchase a $500 notebook computer, and could think "What a great deal", but in reality it could be lacking a whole lot. Just because a salesperson says it's good for whatever doesn't mean it is. With the exception of Macs and custom machines, like you said, you may not get the best deal, but I think that if you have a better understanding of what you are looking for and you go the online route and configure a computer as much as you can, you'll be set.
Technology will keep advancing, and today, computers do almost everything we may need them for. As long as there is a need for speed in computers, the market will keep growing. If you're fine with the performance of current machines, great. But you also know that it's only going to get better in the future, and the lifetime of your machine would be the only factor in holding you off from buying a new one. From that point of view, you are in control. That there is sensible, right?