While Intel has opened the source code to their current driver set, it should be noted that the Graphics Accelerators (GA) themselves lack hardware typically found in other GPU's ( mobile : http://www.techarp.com/showarticle.aspx?artno=98&pgno=3 / desktop : http://www.techarp.com/showarticle.aspx?artno=88&pgno=19 ). The result is that the card's depend on software rendering in order to do the same task as a normal GPU. The combination of software and hardware rendering places the Intel cards on the more scathing criticism from professional game developers.
One of the reasons why Intel GA's are so prevalent is due to the heavy use in business and mobile sectors, where nobody ever quote, "got fired for buying Intel." Same people never quote, "Got fired for buying Microsoft" either. The fact is, the market that Intel's GA's cater to isn't interested in buying Linux. They are interested in the status quo, nothing changing.
It should also be noticed that Intel does NOT have a policy on whether or not future integrated graphics will have open source drivers. Personally, given Intel's creation of HDCP, EFI, as well as the lack of any assistance to the OpenBios/LinuxBios projects, or assistance to the Intel Azalia Spec audio driver project, I think Intel is still better classified as Open Source Hostile.
By the same token, Intel has no policy if any future discrete graphics cards would have Open Sourced drivers.
Something to think about before you promote Intel's products.