Jetstar are offering a service based on low individual margins and high turnover. If you want to save your money they give you the opportunity to do so provided you follow their well publicised conditions.
If you want better service/more flexibility there are other options but they cost more money.
Virgin offer flexible tickets ,but not for $49 .QANTAS offer Business class on alot of routes for several hundred dollars.
You generally get what you pay for and there simply isn't the margin in a dirt cheap fare for any more than getting your bottom on a seat. Suits some people fine ,others expect too much for too little.
Pay more or accept less.