Celebrim
Legend
Sure the other pillars can be risky, but I find the risk doesn't seem as immediate or dangerous as combat.
I'm going to stop the quote there, though the rest of your discussion is interesting. The reason is that the rest of your discussion goes on to undermine the very idea you start with, and I'm going to try to explain why.
The answer is ultimately encounter design, and in particular the difficulty of making a good non-combat encounter relative to the difficulty of a good combat encounter.
Consider the following:
a) A combat encounter can use off the shelf components. You can mix and match these in a near infinite number of ways - orcs riding triceratops, hobgoblins with pet hellhounds, and so forth. Each provides its own unique challenge.
b) Monster components tend to be lavishly detailed. 4e in particular just lovingly crafted monsters as interesting combat playing pieces. Compare with the focus it did on the non-combat abilities of monsters or on off the shelf environmental features.
c) Combat encounters are spatial and tactical, providing intellectual interest in and of itself without conscious effort on the part of the designer.
You can have bad combat encounters and good non-combat encounters. But it takes less skill to have minimally entertaining combat scenarios, in part because the work is harder and in part because less of the work is done for you.