First, lets understand what we mean by models. We will restrict this discussion to digital ICs. There are at least three distinct types of models system designers might need.
Signal integrity models are needed to verify that the traces connecting the different parts on the board and across the backplane will carry the signals from chip to chip without introducing so much distortion that the receiver will be unable to correctly interpret its inputs. This type of model is usually supplied in IBIS format but may also be in Hspice or VHDL-AMS. IC companies do a fair job of providing these.
If an IC incorporates JTAG, it should have another type of model that defines the JTAG boundary scan chain. This type of model comes in a language called BSDL and IC companies are quite good at providing them when appropriate.
A third type of model is for functional simulation. A few IC companies do an excellent job providing these, most IC companies are fair to poor at providing them and, some companies do not provide them at all.
Why are simulation models important? What do engineers do with them? How can the IC industry do a better job supplying them?