Others have tried arguing with you, but I'll make this very plain and answer your questions bluntly, since you seem to lack some of the knowledge they assume you have.
It's not a ripoff - they are selling consumers exactly the performance they are promising.
Manufacturing isn't perfect. They test at the factory to see if each chip can run at the promised core count and clockspeeds. Fairly often, particularly with top-of-the-line chips, a few cores will be broken, or unstable at the specified clock speeds. They are unfit for sale as the originally-designed product. Rather than throw it away, they disable whatever is broken (either in firmware, or by blowing fuses built for this purpose on the processor) and sell it as a lower-cost, lower-capability product. This is standard procedure for everyone. Just off currently-sold chips:
For Nvidia:
The 970 is a 980 with 3 SMMs disabled (out of 16)
The Titan is a Titan Black/780 Ti with one SMX disabled (out of 15).
The 780 is a Titan Black/780 Ti with 3 SMX disabled (out of 15)
The 760 Ti is a 770 with one SMX disabled (out of 8)
The 760 is a 770 with two SMX disabled (out of 8)
The 745 and 750 are 750 Tis with one SMM disabled (out of 5)
For AMD (GPUs):
The 290 is a 290X with four CUs disabled (out of 44)
The 280 is a 280X with four CUs disabled (out of 32)
The 265 is a 270/270X with four CUs disabled (out of 20)
The 260 is a 260X with two CUs disabled (out of 14)
The 240 is a 250 with one CU disabled (out of 6)
Note: I wanted to include AMD CPUs as well, but I can't find perfect info on their CPUs. They are clearly using binning like everyone else (probably more, if their Phenom II days are anything to go by), but I can't tell you exactly which ones are stripped-down versions of which.
For Intel (CPUs):
The 5920K is a 5830K with 12 PCIe lanes disabled (out of 40). Both of those *might* be 5960Xs with two cores (of eight) disabled.
Every current desktop i5 is an i7 with hyper-threading disabled. Likewise, any current desktop Celeron or Pentium is an i3 with hyper-threading disabled. For the most part though, Intel only bins based on clock, not cores - if it's a low-clock version of a given chip, it likely tested unable to run at higher speeds with stock voltages and cooling.
Oh, and every single PS3 processor had one SPU disabled out of 8. Processors with all 8 functional were used in certain IBM servers, amongst other things.
If you want a car analogy, imagine you were sold a car with a 4-cylinder engine. You check later, and find a 6-cylinder engine block, but two don't have piston heads in them and don't run. When you get some spares and try to run them, you find the two cylinders have completely busted sealing, and they contribute no power, only noise and pollution and a nasty rumble.
When run exactly as you were promised it would run, it works perfectly. The extra cylinders affect nothing, because this is a metaphor and the actual physics of a car don't apply. They used a part to a higher-end car that would not work in said higher-end car, but they neither told you that it would, nor charged you as if it did. They actually probably charged you slightly less than if they had built it as a four-cylinder engine to begin with.
For this story, imagine some unscrupulous car dealer (also known as just "a car dealer") took that car, put the pistons back in, and sold it to you as the higher-end car without letting you test-drive it to find out that it doesn't actually work, only letting you pop the hood to see that it has all six cylinders. The car manufacturer then changes their procedures so that instead of simply removing the pistons, they actually fill the broken cylinders with steel to prevent it from even pretending to work.