Definitely. Indeed, I'm not saying that there isn't something of a standard already. But in interactive fiction, context and nuance can make or break a new player's experience. In many cases, it only takes a single misunderstanding to bring a game to a halt.
Using my own experiences from the last 12 months as the example...
There are a number of commands that have never stumped me since I (re)discovered interactive fiction. A few examples would be "INVENTORY", "SAVE", "LOOK". These commands have worked exactly the same way in pretty much all of the games I've played.
Then there are those commands which are undeniably linked to an action but, due to the context, I've been stumped in using them. Surprisingly, they include compass directions. Yes, I know that the abbreviation "NE" is north-east, and that the command syntax never changes, but I remember one section of The Dreamhold where I spent an hour lost and wandering around because I misunderstood the description of a curved passageway. It said something like: "The exits are east and west from the passage, which curves round and ends to the northeast." I kept going east and west, but didn't understand northeast was also an exit. In this case it was the application of context, not the command itself. So, while I can be taught that "NE" is northeast, I also needed to understand how Zarf uses narrative.
This thread mentions some other perfect examples. "EXAMINE" where "READ" or "SEARCH" or "FEEL" is intended. Getting on or in things, or trying to make things work with each other, continues on occasion to perplex me. In the IFCOMP 2010 game Ninja's Fate I temporarily struggled to find the right syntax to attach the rope to the grappling hook, the grappling hook to the open trapdoor and climb down the rope inside the museum. It's a simple action, which I can describe many ways in plain English, but the correct implementation of commands seemed to elude me.
And you're right: conversation is the real killer. I think I have yet to have a complete conversation with an NPC that worked exactly as I intended. And given how many games are now striving to have a populated game world in order to create further immersion, that means a certain level of frustration is becoming increasingly inevitable (at least, for new players).
On the topic of deviation, I have to disagree. I think that while many games use a similar set of commands for most of their actions, almost every game these days includes something new. Maybe not an action to go to the toilet, but something. A new twist to doing things, a new way to reference something, a new type of object or puzzle that works a little bit differently, a new exception to the rulebook. Otherwise, we'd all just be using the commands examine, get, drop and attack, etc.
(Speaking of which... "ATTACK" is another good example. I'm holding a light-saber, but when I type "ATTACK STORMTROOPER" do I really mean that I want to rush at them with my bare fists? I can't remember which game it was, but I recently died from doing a similar thing.)
Perhaps you are right. Perhaps it is all a matter of indoctrination. But I still can't help but wish there were a range of games--even just a series--that played the same way. A series where, once you knew how the first one worked, you didn't need to learn new commands or actions or realign to a new author's intentions to play the rest.
Then again, maybe that's just me.