Debian always got this criticism of long release cycles. 2 years in development of GNU software is revolutionary, but still Debian continues to churn out new stable distros at a snail's pace.
But actually, in my experience this kind of cycle is good for casual users who require only a few set of software to survive instead of complications like the latest DE, software or Window manager.
In KDE and Libreoffice at least, it happens that after each upgrade, there's a regression. And you know those regressions will be ignored long to cause major annoyance (you know the KDE devs will be implementing 'features' instead in their 6 months release cycle), and ultimately these buggy updates with regressions will be pushed to unstable and testing... and nothing can stop it from being pushed.
So, after each update of the distro, there's an element of surprise.
But the sable branch on the other hand will remain with the old version, the few tolerable bugs that existed will continue to exist and people will find workaround for them, and many times the fixes will be backported and updates will be provided, then for the newer software we have the backports, the only problem with them is that it's difficult for the average joe to install form backports. Maybe Ubuntu software centre should be modified show graphical packages form backports also.
Also drivers and kernel can be backported, solving most of the hardware compatibility issues.
People who ask for comparatively newer packages (5%) can usually handle the small inconvenience with testing, but not the average non-IT guy.
So ultimately: Debian's stable's release cycles matches the average user's requirement of a stable and secure desktop.