iPhoto: Why modified date instead of creation date

After I switched to my beloved Mac, I imported some very old photos from windows to iPhoto. They had been opened and rotated in windows photo viewer. Therefore, the modified date was different from the creation date.

iPhoto sorts them according to the modified date and this messed up my iPhoto Library.

I have tried the iPhoto "change time and date" feature, but that is not a good solution.

Could anyone please help.

This problem has been haunting me for more than 6 months.

Please.

Thank you very much.