FeiGnt :
I'm not sure if I just haven't done enough research but I haven't seen many i3 or i5 models or rather any mainstream laptops available with the technology.
At the moment, there are quite a few laptops out now that utilize 4th-gen i7s, a few that utilize i5s, and none that utilize i3s as they have not been released yet.
Some laptops with Haswell processors: The new Macbook Air, some MSI laptops, and perhaps one or two more companies.
It is used, but you are correct; the technology is not being fully used by the producers.