It would be nice if these were offered with a streaming option. ( I didn't see any streaming on their website.) None of my computers even have a disc tray anymore. I guess I could watch them on the TV, but maybe it is time for the train hobby to catch up with the technology.
IIRC, TM has a way to view their videos without actually having a physical disk. I've seen it listed on their website, but didn't pay too much attention since it's not my preferred method.
Personally, I like having a disk for a couple of reasons. Unless I lose or destroy the disk, it's mine forever - no worry about a website going away. DVDs are so widespread that I doubt there will be a lack of hardware for playing them in my lifetime. And I like sitting down in front of the TV and watching the trains - bigger picture and better video than on my computer.
I also enjoy watching video of layouts that I've seen in person - it's interesting to see the different perspectives and details that I missed.