I'd agree with this, though I'd argue the main reason this split exists today is because as Melbourne has grown outwards in the last 40 years, there has been little serious investment in developing rail capacity to support those outer suburbs. Instead, the government chose to build freeways.
This. People are stupidly allergic to splitting municipalities but the fact of the matter is that the poorer municipalities in many cases would be better served spending their tax dollars on themselves rather than throwing it into some bigger pot and mostly getting told by the richer portion of the city exactly where/how it gets spent.
Some trams go further than the distance that anyone I know would call "inner suburbs".
Bundoora, Preston, and Box Hill to the north, Surrey Hills to the East, Carnegie to the South. (I don't think anything goes West further than Maribyrnong?)
All suburbs, more than 10km from the city, full of people who work 9 to 5 in unglamorous jobs.
Sure, it's cheaper further out, in places that will take over 45 minutes to commute from... but that's the case everywhere in the world, as far as I know. And it's not like Melbourne doesn't have a bus system to rival Sydney's.
The trams are a part what made the inner city areas attractive to the wealthy and drove gentrification, but that's only a recent trend, when the lines were first built and for most of their lifetime the areas serviced by the tram network were working class suburbs.
Even now many of these areas contain a lot of less wealthy people, jump on any tram and you'll see just about every demographic represented.