I wonder whether it shows that our understanding of the underlying concepts is poor? A highway is, in the end, defined for people, not vehicles. Therefore, the custom that those going straight ahead have priority applies to all road users. Over the years, we have gradually developed footpaths/pavements (for pedestrians) and paths/lanes (for cyclists) but, in the absence of other factors, it's hard to see why using those would change the basic principle, because they remain part of the highway (otherwise, how could the Highway Code apply?)
So, the long-standing and widely-ignored rule that a pedestrian crossing a side-road has priority is because that pedestrian is a road user on the main highway. There's no special treatment; rather the reverse - the pedestrian is simply being treated in exactly the same way as if that pedestrian were driving, because the choice of vehicle has no bearing at all upon one's rights.
And hence the point that this is not a change in the law, but a change in the guidance to make the law clearer.