Some stand alone DVDplayers also have issues with certain discs but most of DVD movies play OK. You can emulate things to certain point, but there are some differences in firmware level between certain DVD players and computer drives which are harder to imitate.
You can slow back optical drives with tools like Nero CD/DVD speed but I am not familiar any DVD Video protection that would use drive speed as protection.
Those companies that manufacture these discs circumvention tools usually analyze problematic discs and figure out how to circumvent those protections. You could supply patches to VLC, but taking money would be a bad idea.
What does the error message say?
And you can try nightly builds, if they handle those discs any better.
http://nightlies.videolan.org/