Peter, I should imagine it has something to do with the much greater lubricity of diesel - it is kinder to high pressure fuel pumps and injectors. Petrol by contrast has no lubricity which is why it needs detergents and other 'premium grade' additives to work well in GDI engines (and even then the long-term wear characteristics are unproven)
For anyone contemplating a future upgrade path on a petrol engine, they might want to bear in mind that in-cylinder high pressure injectors can't be re-sited in throttle bodies - that would be enough to put me off!
