Until GTPlanet post it, it aint anything more than weak gossip.
Theres no way PD will go to E3 (June 15-17, so 4wks away) and announce GT5 coming out the same month, no way, not buying that. With 2-6 weeks till this completely fictional Asian release date, it'd be stupid to have not made a song & dance about it coming out then because im sure they'd love to make that announcement as they must be aware of the friction the lack of a release date has on its fans.
They wouldnt make any important announcements right before E3, seeing as its the biggest games expo of the year... it just doesnt add up, not within such a short timeframe and so close to E3. It'd be bizarre to wait for E3 and give nothing away till it was stupidly close to a regions release date, and it'd be very uncharacteristic of Sony to let them announce a Asian release date go when they'd rather hold off 1 surprise they could save for E3, afterall we go to E3 these days with 80% of the information given either already announced, or leaked in the week leading to it, Sony joked about the fact that official video of the PSP Go was out before they'd even announced it at E3.
It'd also be odd given recent comments saying the game is 90% complete, then a month later announce its gone gold and being shipped.
I'd expect mid November (Asia) & late October (US & Europe)... if we've all been good boys & girls for santa, and i'd expect the annoucement to come at E3 or worse the Tokyo game show in mid September and a later launch than above.