More than the operating systems, it’s the applications that start requiring more and more processing capacity, RAM and other hardware.
I’ll take your example. 10 years back, you had a brand new laptop, you were using Ubuntu 10.04 and everything was perfect.
Ubuntu used GNOME 2 back then and GNOME 3.28 desktop today. Do they have same system requirements? No.
It’s not that you cannot run Ubuntu 18.04 GNOME on a 10-years old laptop. You can but it won’t be the best experience because the desktop environment itself will consume a lot of resources. Run a few applications and you’ll have CPU running at 100% and perhaps you’ll have an unresponsive system.
How would you know when your system is incapable of running your system? First sign, your system is gradually sluggish with each updated version. Second, there is updated system requirements from the distributions.
So, let’s say you had 2GB of RAM back in 2010 which was decent back then. By the time you were on Ubuntu 14.04, you started noticing that your system is not as smooth as before. By Ubuntu 16.04, you’ll have a real hard time running on 2 GB RAM. Ubuntu 18.04 comes and the recommended system requirements is 4GB for physical install.
You take the hint around Ubuntu 16.04 and switch your distribution.
Yes, that’s one advantage of using Linux. Unlike Windows, you are not restricted to just one operating system. If your system is getting old, you can switch to a distribution that is tailored to consume less resources by the use of a lightweight desktop environment and a suite of lightweight applications.
Unless there is a significant difference between the minimum hardware requirement and your system’s hardware, you’ll get the upgrade to the new version. However, if you barely qualify the minimum requirements, you should start planning your switch to a lighter Linux distribution.