From what ive read on the Redmond Pie website, the real reason the white phone has been delayed/axed is due to the fact that too much light was captured when taking pictures. This could only have been fixed by redesigning the phone.
Text taken from the website:
Real Reason: Light Leaks
Cult of Mac reports that the real, actual 100% fo-sho’ reason behind the delay was not the discolored buttons but actually because of “light leaks”. Explanation below:
When the white iPhone 4 takes a photograph, the semi-translucent glass cases leaks extra light into the camera which absolutely ruins photographs. Cult of Mac’s source said, “You don’t get accurate pictures on the white iPhone because of the color of the glass back. It washes out the pictures”. The source also said that Apple might have to do a complete redesign of the white iPhone 4 to deal with the light leaks.
The issue was discovered after a “last minute test” at a secret facility when the white iPhone 4 was used with a third-party case. Apple, of course, wouldn’t let an imperfect phone out.
Link =
http://www.redmondpie.com/white-iphone-4-cancelled-rumor/