There is a very nice discussion of the point about the work of Webb et al. at:

http://www.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

And another at:

http://en.wikipedia.org/wiki/Fine-structure_constant

Note that Webb himself emphasises the conditional nature of the result and other researchers still are evaluating methods, results, and implications.

The speed of light in media other than vacuum has nothing to do with the matter; photons keep getting absorbed and re-emitted and generally interfered with by matter.

As someone has put it, the reason that nothing travels faster than light is that nothing travels slower than light, including you and me. The resultant vector of our speed through time and space is always c, whatever c may be, which always is the maximum speed at which information can be transmitted.

Because a photon has no mass it cannot travel more slowly than c and so its journey through time is Zero. From the point where a photon forms, to the point where it is absorbed or converted, it's subjective duration is Zero.    

In fact there are limited circumstances where things do, can, or might travel faster than light.

If you just remain motionless in space but the space itself is stretching out, the distance between you and another thing can become greater at a rate that exceeds lightspeed.

In the equations of relativity, mass becomes infinite at the speed of light, so only massless particles such as photons go at that speed.  But the equations are no longer infinite if one goes even faster than that, although one's mass gets multiplied by the square root of minus one.  Physicists have hypothesized faster than light particles and call them tachyons.  Although no longer of infinite mass there are still problems with causality and the flow of time for such particles, if they exist. 

You might wonder what a mass multipled by the square root of minus one means and how that could exist.  It's a bit strange as ideas go.  But in physics when a spatial variable gets multipled that way, it becomes timelike and vs. versa.  So perhaps it is possible for such a mass to have physical meaning, since after all, both space and time exist.

But here's something that does seem to indeed go much faster than light: the quantum tunneling of particles.  This is a situation where there is an energy barrier or "wall" that in the classical sense should forbid the passage of a particle, yet it "just appears" on the other side due to the Heisenberg Uncertainty Principle, which says that you can't know its true energy all of the time exactly. If you use microwave photons, this tunneling can be over the better part of a meter in length! By modulating those microwaves with a signal, that information might be sent faster than light over that distance (some people argue this isn't so.  They say the photons tunnel very fast but the information flow is limited to lightspeed.)

Also, going back to classical electrodynamics, Maxwell's equations (that describe light and how fast it goes) also have solutions that are not wavy in nature (those solutions are exponential rather than light's wavy sinusoidal description).  In those solutions, the electric field effects go faster than light.  In antenna engineering one speaks of the "far field" or the "near field" behavior of the antenna.  The far field is the wave-like propagation of radio waves to and from great distances from the antenna--what the antenna is meant to do.  The near field does not propagate very far, but its effects can exceed the speed of light.

Finally, quantum entanglement ("spooky action at a distance") is that weird phenomenon whereby a pair of particles gets created such that they have a quantum state relationship, for example that if one particle's spin is "up" the other must be "down".  But at the time of creation, the states are not yet determinate: they can later assume any state but are linked in some ghostly fashion.  These particles can be lightyears apart, and if the state of one particle becomes determinate, then instantly the other's does too.