Does Amazon ALWAYS ship DVDs with their corresponding slipcases (I mean if the movie indeed has a slipcase of course as indicated on one of the threads here) or do they sometimes not?

Just curious, thanks!

Depends. When a new movie is released, the initial batches from the manufacturers come with slipcovers. In this case, Amazon ships it w/ slipcovers. However, after some time, the manufacturers release the DVD's w/o slipcovers so Amazon ships them w/o covers as well. This is the same for B&M stores.

If slipcovers are that important to you i would order the DVD close to the time that they are released. After a few months, you might not be able to find them w/ slipcovers.

This has been my general experience with Amazon. I get slip covers for movies that have been released fairly recently, if they have it.