that different Makes & Models of DVD Drives work in different ways.
Quite often the technology is changed between different models in the same Product Line or even different makers can chose how well that they stick tot he DVD Standard. Where a DVD Drive that has more Power in the Laser Beams may read a Disc it is quite possible that a Drive with just the Minimum Power Laser Beams may not read the same DVD Disc.
Then when it comes to recorded Disc's there are lots of differences in the Dye Lots used by different makers of the Blanks. So it's possible that one color Dye may not be readable by a DVD Drive with it's own Color Laser but it is perfectly readable by a different Make or Model DVD Drive with a different color Laser.
Back in the early days of Recordable Cd's many makers would make CD Recorders that could only read the Disc's that they made and not read or record disc's from a different maker. Kodak used to be very well known for that back when we where paying $25.00 per Disc for each & every Blank CD.
Computer Optical Drives tend to be closer to the Standard as laid out by Phillips where as DVD Readers for things like TV's tend to be open to a lot more formats and just be able to read all Disc types. This stops them getting returned as not working for the customers needs, where as Computer Drives are not expected to be as flexible particularly if they are Burners. Also Computer Optical Drives can tend to only read Specific Type/Format Disc's like some can read DVD +R but not DVD -R or maybe even DVD RW Formats.
You can find out what Type Formats the Computer Drives work with by removing the Drives from the computers and reading their Specifications on the Label on the Drive. This will tell you what Formats the Drive is capable of reading. ;)
Col