Hi Legbiter,
Being a "designer" myself, I (somewhat) believe in keeping up with the latest trends. It's like comparing previous versions of Windows to Windows 8.
Personally, I absolutely hate a design I made after seeing it for a few months. I feel that it could be better and that it can be nicer.
Chrome, IE11, Foxit Reader, and many of my other applications have changed their design patterns to reflect new trends. Just recently the right click in Chrome is now flat and Foxit Reader now has a flat interface by default (like Microsoft Office 2013), etc.
I rarely (if ever) open avast!'s user interface. But when I do, the simple user interface makes it quick to see where things are. The big buttons, I assume, were also added to reflect the increase in touchscreens.
~!Donovan