I don't know how good that GAME website or whatever is, but I'm pretty sure GT5P is coming in April. April 15th to be exact. At least that is the date for US, and for some reason I don't see Europe getting it earlier.
Gran Turismo 5 Prologue for PS3 - Gran Turismo 5 Prologue Playstation 3 - Gran Turismo 5 Prologue PS3 Game