Just addding to what Nagol said:
No - the player decided we'd be addressing that them when s/he introduced a PC afraid of snakes.There certainly is increased linearality. If I know a PC is afraid of snakes, and I include snakes, I've decided we will definitely be addressing that theme.
Non-random? Yes. My preference? No, it's the player's preference.That is obviously a non-random situation that has nothing to do with an imaginary world and everthing with my preference for a particular story element.
I don't see how playing to the preferences of those at the table is a disadvantage. It's the whole point of the way that I like to play an RPG.The disadvantage is that it is distinctly biased, which means playing to GM and player preferences and away from the unknown.
I didn't put the PC on that path - the player did.The fact that I create space for the unkown ("Will the PC flee?..." etc etc) does not negate the fact that I have the PC on a linear path toward an encounter of my preference
Well, that really is up for grabs, in my view. In my experience the outcomes are less predictable when the situations put at stake conflicting values/concerns/themes with which the players are strongly engaged. The elements that make up those outcomes are predictable, of course - the PCs, the snakes, the Orcus cultists etc. But the way it resolves is up for grabs. Again, I refer to the Paul Czege quote posted upthread for elaboration of this point.a range of possible outcomes that is substantially more predictable than an encounter with less tailored content.