I understand your point from your perspective however I have more of a broad view on the subject. First saying an iMac isn't a gaming machine is typically fluff for saying it's not a powerful machine since that is basically what a gaming machine is (an machine designed to handle constant graphical task as fast as possible).
Fair enough. However, you're basically talking about sustained heavy-load performance. Most work that the iMac is popular for (design, photography, illustration, etc) requires burst type performance where throttling is not an issue. This is the reason why OS X users, when they need sustained power (for, say, video rendering) - they get a Mac Pro.
Now, I understand what you're saying - make the thermal properties of an iMac better (by changing the design) and you get better performance for - theoretically - the same price. But it's not that simple. The reason why Apple can offer this killer display and build quality is because the iMac is popular and they can produce it in larger volumes as it finds its audience. That means they have to provide a machine that will cater both to people that need performance and to people that actually care about design, size, general 'feel' of the computer. Apple has been working like this for years and years - they make something that has that "cool" factor. While making a computer that is thin and elegant may not mean much to you, it sure means a great deal to a lot of people who don't really measure heat of a CPU or GPU while running a benchmark. A computer you want would not seem magical and fancy and 'shiny' (or whatever derogatory term people use here to describe these things as if they don't matter to anyone - while, in fact, they do).
And, let's be honest, it's not as if the iMacs are not powerful. I mean, I'd totally agree with you guys if the iMac would barely run apps, but in fact they are really, really fast. All the reviewers say it's fast too, I'm not making this up. I have an i5 5K and I am yet to see how my computer is somehow slow in anything. As I said, I have large PSD files open all the time, I use Zbrush, I use 3ds Max (in Bootcamp) - the thing flies. 3ds Max is not a lightweight program, let me tell you. Sure, there are some workloads that require farms consisting of large towers - but what kind of work is too much for a new iMac? Seriously, I'm asking - is there anything, other than gaming, that you think the iMac is inadequate for?
The way I'm seeing, you're trading some benchmark-only performance in most of tasks for dramatic improvement in how the computer looks and feels. That screen, that futuristic look, that silence, that computer that looks like it's from the future - and that Apple can make because, you know, people will actually buy.
I don't know guys, I just love my iMac. For me, measuring the value of a computer by just looking at the specs is like valuing a car just based on the horsepower of it's engine. Sure - if you want to race - that is by far the most important thing. But for the rest of us, there's something to be said about how the thing looks and feels.
