We usually claim that stress is a transitive verb, so there is no need for a preposition such as on between stress and its object. And, on page 69 of my book on Brunei English published by Springer (here), I claim that the following extracts from local newspapers reflect Brunei English usage:
The driving schools are also advised to stress on the importance of patience ...
The minister stressed on the importance of paying attention to the field of science and technology ...
However, today I saw the verb stress followed by the preposition on in an article about the visit of the Australian PM to Indonesia in the BBC World website (here):
This makes me wonder if the usage is becoming the norm. It is just the sort of change we would expect to take place in English, as it regularises the grammar by making the verb stress behave like the noun. Furthermore, one can focus on something, so why not stress on? Maybe Brunei English is leading the way with the evolution of English!
