You will need at least two different players in order to fully enjoy a DVD collection. It's sad but true. Even if you say "I've got 3000 DVDs and never had a single problem!" the next one you buy could be the one.
DVDs are based on software/hardware, much like a computer. They aren't simply made of a single industry-wide standard. So, some hardware (players) are going to have issues with some software (discs). That's just the way it is.