Debian is known to be rocksolid and stable. The software included therefore is older than upstream because its extensivly tested. Bug fixes are usually backported.
To make it easy Ubuntu is a Fork of Debian, mostly unstable or experimental branch, adds some fancy desktop stuff and label it stable.
Also Ubuntu maintains only a fraction of the packages includeed by themselves. Most are in "universe" and "multiverse" repositories which are community supported. If a package maintainer decides to no longer maintan a piece of software then you are on your own because nobody official will care.
Also the advertisment von Ubuntu to have five year support is kind a BS, because if you take a look at Debian you will notice and do the math with LTS you will also get five years...