I don't see how I'm generalizing. I'm observing that you'll probably have more time in your life to spend at home than you will ever have on the road, so that time should be used wisely.
Every place you will visit will have its entertainment alternatives, and you will expand your horizons if you try them out, if only to see how similar and different they are in comparison to those that you have at home. Virtually every country in the world has cinemas, so go watch a film in one of them, instead of lugging around a device that should get very little use if you are getting the most out of your travels.
In any case, if you are staying in hotels, they will generally have televisions and video networks. If you are hosteling or staying in guesthouses, many will have a TV or video room where you can chill and watch something. It's not as if television and video don't exist outside of Europe and North America.
I don't wish to be a Luddite, but I believe that turning the current generation into a confederacy of vidiots is not a great idea. You can use down time to read a book or newspaper, (re)learn the art of conversation, or do a whole host of other things. I traveled for two years without ever feeling the need for a DVD player -- there were so many things to do and so many great people to speak with, why would I have bothered?
As for using them on public transport, if you are going to use it, then please bring headphones so that you don't annoy those of us who would prefer to have a conversation, look out the window or read a book.