There are still a few cathode ray tube monitors out there being used, for anyone who has one of those a screensaver is quite important because turning the monitor on and off isn't going to extend it's life, making it transmit pure black is a better option but a bit dull. I used to use a clock screensaver to shake me out of daydreaming when I had deadlines. There are rather a lot of interesting screensavers, some of the ones which are associated with shareing unused resources are well worth looking at. This I like http://setiathome.berkeley.edu/sah_graphics.php
I'd quite like to have something like stellarium kick in when a screensaver would have done just to help maintain context.
Currently I don't need or use one, however having something useful kick in when the computer is idle is still a good idea; interuptable scans, shared tasks and so on. Graphics to go with that might even be useful or just eyecandy, either way I hope the option to use a screensaver remains even if it isn't on the disk.
Part of focusing on innovating the new is bound to be depreciation of the old especially when size of storage medium is a factor, so it's swings and roundabouts. As a fortunate online person this is not a problem, gimp is one of the first things I install for example, though I'm aware that for many less fortunate what is on the disk is more critical. Internet cafes often charge for downloads and if the iso's and debs don't work there is no connection to easily sort things out at home online.
According to the old Ubuntu ethic screensavers would be on the disk as the people least likely to be online are most likely to be using a crt monitor.
That said the Ubuntu philosopy has changed; providing a free alternative operating system for those in the third world is no longer a key factor, now it's solidly aimed at the well to do who can afford to have recent hardware. So I suppose people using old hardware won't be able to run Ubuntu anyway, just think ram.
I miss the old Ubuntu ethic but the distribution did help to popularise the linux idea and lightweight distro's have come in to fill the gap. The new ethic is important too, innovation does matter and it is logical that one of, perhaps the, biggest development teams take on that role.
Ubuntu could easily be first to produce a working holographic display and should that happen expect flames about the decision to drop old physical screen features. A couple of decades after that those who flamed will probably be using the results of all that holographic development but leery of the brain induction UI.
I still feel that Ubuntu is a lightweight alternative to Windows, at least compared to Windows 7. I didn't realize how ram heavy 7 was until I switched back to Ubuntu.