I wouldn't quite say "equally". Jakarta is a melting pot and the most significant portion of the population there is of Javanese descent. But many many people who are of Javanese descent don't even speak Javanese, especially if they were born in Jakarta or in the western part of Java.

It seems likely to me that people who are speaking Indonesian as a first language (e.g. Jakartans) have a substantially larger vocabulary than those that are speaking it as a second language (e.g. Yogyakartans). I would presume so, but that makes me wonder what the source of that larger vocabulary -- Malay? Javanese? English? Other languages native to the Indonesian archipelago? All of the above?

> It seems likely to me that people who are speaking Indonesian as a first language (e.g. Jakartans) have a substantially larger vocabulary than those that are speaking it as a second language (e.g. Yogyakartans).

They are speaking Indonesian as a second native language, they will acquire Javanese and Indonesian at the same time but use Javanese in conversation and Indonesian when consuming TV, books and in school. So their grasp of formal Indonesian is going to depend mostly on education level.

As for colloquial Indonesian, due to the internet new colloquialisms spread much more rapidly to other parts of Indonesia. So it probably depends on how old said Yogyakartan is.