Graph from the RTA.
If you ask me, this has nothing to do with the cost of cycling - you don't need a $5,000 bike and lots of fancy equipment to go for a ride. Instead, this has everything to do with attitudes to exercise and obesity. I'll see if I can find a graph that shows obesity vs income - I reckon it will be the reverse. It's well known that the poor suffer much more from diseases causes by eating, drinking and smoking too much and exercising too little. In the old days, the poor were skinny and the rich were fat - now the opposite is true.
The above graph probably holds true for exercise activities that cost next to nothing - like going for a walk or a run.
It's interesting to note the reactions to Tony Abbott and all his cycling of late. Much sneering has come from the Labor party, which supposedly represents those at the left of the spectrum on this income graph. In the old days, this mob would have sneered at the nobs as they cantered past on their horses or in their landaus. Now, they sneer from their recliners as the nobs jog, swim or ride past