That seems to be an explanation, although it seems weird that you can already create a more powerful (in terms of flops) machine with a number of GPUs that is affordable for a hobbyist. Maybe raw processing speed is not the most expensive factor in supercomputers anymore? That weather forecast thing also has a huge amount of RAM, and probably some high-speed inter-computer connections as well.
That is it. A hobbyist GPU "Supercomputer" made up of mining rigs would only be useful for problems which have no inter node depndencies, little bandwidth, and no storage requirements. Essentially completely useless for anything other than things like Bitcoin hashing or password cracking.
Most problems in the world are complex and weather modeling isn't hashing an incrementing nonce value each of the nodes is doing work which depends on other nodes. A mining rig would simply fail at that. Still it is strange they didn't use GPU in the super computer to boost the more computationally intensive portions.
I used an exchange rate of about 4EUR/BTC, so your value would correspond to about 160 EUR/day.
If you are correct, then how is that possible? Wouldn't they be able to have more FLOPs than they report even by doing emulated floating points on the Xeons?
Or does bitcoinwatch.com use an unrealistic estimation of the FLOPS / hashes ratio? I see in an earlier post that they use 1 INTOP = 2 FLOP. So it assumes integer is actually slower than floating point? But even if it is 4 INTOP = 1 FLOP for floating point emulation, you'd still only lose a factor 8, which is less than needed to explain the ratio between 12 EUR/day and 160 EUR/day.
(*) I did some speed measurements on an ARM 7 without floating point unit and a Pentium 3 or 4 with floating point unit. On the ARM, emulated floating point operations (addition and multiplication) were actually faster w.r.t. integer operations than the hardware-accelerated floating point w.r.t. integer on the Pentium (TfloatARM / TintARM < TfloatIntel / TintIntel). I did not use things like SSE on the Pentium.
There is no Universal ratio. The ratio they used is relevant only for AMD 5000 series GPUs. On any other hardware it is completely off and not by 10%, or 50% but 1000% or 20,000%. It is really ony a guestimate and shouldn't be taken as a serious value. Nobody rates supercomputers in intops. If they did one could simply post the intops of the network and be done.
The * which should be next to the Petaflop numbers should read something like:
"(if the entire network consisted of x000 AMD HD 5870 GPUs. Single precision only, double precision would be 1/4th stated speed).