Hi there,
Wii discs are not exactly DVDs. Nintendo uses a special format that is based on the DVD specifications called RVL-006, most PC DVD drives cannot read this format.
There is a reading method with certain LG drives and a raw dump program. Once the raw data is read out, it can be burned to a DVD+R/RW with a copy software.
In addition to this the original Wii discs usually have a BCA mark on the inner ring of each disc, e.g. a bar code. This BCA mark cannot be reproduced by a DVD writer and the Wii appears to read out this bar code. If the code is not present on the disc, the Wii won't accept the inserted media.
Therefore installing a modchip is necessary in any case in order to play backups. _Of course this is a purely theoretical digression. We don't recommend installing a modchip or a modified firmware on a Wii._
Some links:
http://forums.afterdawn.com/thread_view.cfm/563020
http://forums.afterdawn.com/thread_view.cfm/91/471073#4068289
(Drives)
Regards
Chris