Yeah, same problem here.
I've got an Indian P765 with V10d stock ROM as well. If left idle for sometime, the wi-fi seems to be connected but no data transfer occurs.
The small upward pointing triangle is shown on the wi-fi icon in the notification area, but the data transfer LED of the wi-fi modem doesn't blink, and so no webpage loads.
But if the wi-fi is being used continously, the problem doesn't occur.
Looking forward to a solution, thanks.
Edit: Reduced the Beacon Interval of the Wi-Fi modem to 100ms. The data connection is maintained now.
Problem solved. The phone's working fine afterall.