1. The increase in speed enforcement means that many HGVs now rigidly observe the 40 limit on single carriageways. Because our roads are now so busy it takes a very few HGVs before we are all driving at 40, with a few hotheads attempting dangerous overtakes. If trucks and vans could do the same speed as the rest of us this would not occur.
2. At the other end of the scale, many small vans (e.g. Peugeot Partner, VW Caddy, Ford Connect) are now classed as large goods vehicles (being over 2T laden weight), which means they have to drive 10mph slower on all roads but motorways. This is not well known even to the drivers.
Many cars are now over 2T and even windowed versions of the same vans do not have this anacronistic law applied to them.