I think you’re oversimplifying “simple”. (Bad pun, I know :)
The reason simple came to be so important in dev, IMO is because of years of contending with feature-obese software that needed you to take a few weekend classes before you could start using it properly.
To me Basecamp is simple. This is because I can take one look at the interface and know intuitively how to use it.
Sure, other qualities might rank above simple, but in an age where everything is becoming possible with a single tap or swipe, I don’t think simple is making its way down the list.