Hello

Copy-write law stop, who any ONE that copy and sell DVD movies.
But, people still can use DVD decryptor or DVD backup software and if they want, rip them to compressed video files like .mp4 or .avi.

My main question is:
Why DVD backup or DVD ripper software are not again copy-write law?
Why copy-write law dose not stop these software?

Thanks
There are many problems in the world. The Copy Right Law is just one of many things that some people do not respect.
Better copy protection machines often increase the cost of real DVD copies by the ones that have the right to do it.
And even with the best copy protection software, there are WAYS to still make copies of movies, just of lower quality.

If there wee not Copy Right laws, there would be few high quality movies to watch. The makers have to get millions of dollars back to pay for the time and materials used to produce a really good movie.
 Think about Avatar.
http://en.wikipedia.org/wiki/Avatar_%282009_film%29
Quote

...Avatar was officially budgeted at $237 million....
...On the 19th day of the film's INTERNATIONAL release, it crossed the $1 billion mark worldwide, making it the fastest film ever to do so...

Why copy-write law dose not stop these software?

Keep in mind the person of company harmed by violation of someone else copying their material needs to initiate legal action again the offending party.  If the originator of copyrighted material remains silent, then nothing will be done to help them, regardless of copyright laws.

Copyright holders can ask for enforcement to help them.