Depends Anneee are you looking at exactly the same flight? If so the flight might be full leaving only the most expensive seats. Also lets not forget we are coming into the summer season now which has traditionally meant that seat prices go up to reflect the greater demand.
As many poster have said this is avtive revenue management. Im sure your beloved silverjet didnt sell all their seats at 999 or whatever it was. Only a small percentage of overall seats would have gone for that price the rest would have gotten progressively more expensive.
You do realise that in the current market of high oil prices that all airlines are jacking up prices to cover increasing costs. Unfortunately silver jet didnt do it as well and has folder. This will be survial of the fittest.
PS fuel furcharges to australia through JAL are now running at 1000 AUD or about 440 pounds. Times are changing!