One area they really target is the scientific market, which has more diversity in compilers (see also, Cray, Portland Group etc). icc/ifort/icpc still produce s

One area they really target is the scientific market, which has more diversity in compilers (see also, Cray, Portland Group etc). icc/ifort/icpc still produce some of the fastest numerical code on Intel hardware and tend to support some of the more exotic and cutting edge features first. They also package it as part of an ecosystem, with MKL, TBB, Advisor, VTune etc that help with high performance code. So it's not just compiler optimizations, it's a whole suite of tools.