Captain. It's clearly not true.
Look at the Charleville frequency . The ground station two thirds the way up the marked sector and it's longer than it is wider.
Fly from Oodnadatta to Birdsville and for four fifths of the journey you are on the Oodnadatta frequency.
Examples in sparsely populated areas where it would be costly and impractical to add more VHF outlets.
As
Traffic_Is_Er_Was has said, that's why HF or flying at a reasonable altitude is required in those regions for two way contact with ATS on VHF. Within more populated areas such as the "J" curve, the situation is different.
Believe what you like, but VHF coverage is always the first consideration.