I have a few comments in regards to this because I build PCs regularly. It isn't conclusive that: " Even if you leave out some stuff in your PC build to save money, the time and stress it takes to do it makes the effort equal to a Mac. Therefore, both offer an equal value proposition, budget-wise." This is obviously up to the person.
In regards to this comment: "The fastest gun in the world can maybe put together a machine in a day." I built my very first PC in a few hours. It took longer as I built more, in fact, because I pursued more complicated endeavors such as water cooling, post-build over clocking, etc. which is a feature you don't mention in favor of DIY builds. It isn't to exclusively save money, but to also offer way more hardware features than a build from apple from overclocking, to adding new parts (more local storage), variety of parts (win7 supports more hardware than OSX does), etc.
You mention this: "All I had to do was switch it on, and it works" for a reason you bought a mac PC. Is that not what your DIY builds do? Maybe you're referring to the simplicity of OSX as compared to Win7, but when comparing strictly hardware, all my builds turn on and just work. I've never had issues with the integrity of hardware which is the best part about building PCs: you're in control of the quality and construction of your device.
Finally, you mention the apple price w/o any discounts. You can also find PC parts at a discount via bundle deals or from the numerous sales on newegg, tigerdirect, or NCIX, etc. So, this point when comparing value is moot.
It isn't enough to compare parts. Just because something has the same model name doesn't mean it will operate to the same performance as something inside of a mac. Try benchmarking an iMac PC and its' DIY counterpart at stock settings and check your results. Apple takes special preparation to design the product to be a certain form factor and because of this, certain hardware must be a size other than how it's created at the manufacturer causing apple to ask manufacturers to refab parts to meet their size constraints.
Building a PC is like rigging a camera. You take special preparation to create a PC that meets all of your specifications for the price you can afford while maximizing quality. Does it require work? Sure does! But we spend so much time researching gear for cameras and making sure we get the highest quality picture and sound, why not spend that time on the machine that produces these images? I'm not going to touch on Win7 v.s. OSX, but from a purely hardware POV (just simple performance and features), apple over charges for their equipment and the only logical reason to buy apple gear is what you mentioned: It impresses clients, and also apple is fairly rigorous in their manufacturing so they often construct highly reliable products, albeit it at a higher price (NOTE: the quality of the individual parts is the same. This only refers to construction). However, it is not a fallacy that iMacs cost more than PCs.