Trucks that utilise hybrid diesel-electric drive have been on the market for around 7 yrs at least. There are no really large size units yet, but they will probably appear sometime in the future.
Like all systems it cost versus benifits. The "dynamic range" of the usage patterns can make it difficult. This is no different to small hybrids. The fact you have two different drive trains available, means if your usage pattern is such that the hybrid won't work, you go for the standard model.
Apologies for the thread drift, but the easiest way to get better fuel economy from trucks is to modify the drivers habits, such that they don't go rushing up to junctions and then slam on their brakes, as if fuel was free (well, it is, to them).
Generally correct and has been for decades.
Its the same issue with all technologies, trains drive system, versus road transport etc. Its the usage pattern varience that dictates if a technology will be useful over a product population.
Whats good about some of these "cute" technologys, is that they can be used in a specific market for a decade or so to get data. As material science etc. develops, then the engineering jump into other markets isn't so great.