some nice reading here
http://news.softpedia.com/news/AMD-T...I-267131.shtml

Fearing the hype about AMD’s Bulldozer design and not wanting to risk having its own compiler optimize programs for the same type of SIMD units as the one in AMDs CPU, Intel changes the specification for their FMA instructions from 4-operand to 3-operand instructions.

The change occurred in December 2008, a full half year before AMD announced the FMA4 implementation, but by then AMD was too advanced with their design to make the switch back to FMA3.