Intel thought it had dealt an Ace when one of its boffins presented a paper at the International Symposium on Computer Architecture.
The paper claimed that Nvidia's two-year-old GTX 280 GPU is not, in fact, 10X to 1000X as fast as the eight-month-old Core i7 960 CPU. When it came to supercomputing workloads it was just 2.5- 14 times faster.
The point scoring paper actually made the mistake of admitting that the rival could get a 2.5× speedup on any code which can be installed much cheaper than Intel's top-of-the-line CPU. If it managed a 14 times speed up it would be even better.
Intel engineers were cross that Nvidia was promoting papers that tout a 100 times or even 1000 times speedup from using Nvidia GPUs but one of the things you don't do is admit that they are still faster than what you have on offer.
Generally it would have been better to ignore the Green Goblin and walk away. But for some reason Intel couldn't just shut up.