Well, the MISTAKE miners are making is they are calculating break-even using current or near-term BTC prices. 5-10-20 years from now, assuming mass acceptance, a BTC might be worth several orders of magnitude more than it is today.
The one making the mistake is you, not the miners.
I think Batshit is correct, and you're wrong, Rannasha. My mining equipment has paid for itself - every BTC I've mined in the last year has paid for it's replacement. My HD5870 paid for my HD6970, which paid for the first HD7950, and the 6970 and 7950 together paid for the second 7950. The three GPUs paid for my 11 Block Erupters. I then sold the GPUs for either what I paid for them, or more than I paid for them, and that paid for my two Blades. They're just about to ROI on the power used since I started mining (helped by my PV array).
During the summer my mining rig will be making BTC and costing absolutely nothing to run, thanks to the solar panels. During the winter the heat from the mining rig is heating two rooms in my house, saving heating oil, and using less than 500W from the wall.
So, I'm pretty happy to continue mining for as long as I can, and will probably invest more of my mined BTC in to new hardware in the future. I'm keeping my eye out for used Jalapenos and Blades all the time...
No Rannasha is correct. If a mining rig won't mine as many BTC as it cost, then it's a bad investment vs just buying the BTC. If your graphic cards minted more BTC than you would have gotten by buying BTC then you are in agreement with Rannasha and you made a good investment calculating ROI in BTC terms.