And if you want to visit the city across the desert, travel across the desert seems a reasonable expectation to me. If you want to hire people who are going to kill or die for you, speaking with them also seems a reasonable expectation.
The point is not that it doesn't happen in the fiction. The point is that it dones't need to be played out at the table.
You go looking for whatever the heck you were looking for in the city, but you need something in order to get in there. That something, on investigation, leads to a trail that ends at the desert border. Are you going to go search the desert for this thing you need, as the desert has now become relevant, or bitch and moan that the GM is just forcing us to interact with his setting wank desert to get even with you for your brilliant “avoid the desert” strategy?
I want to know a bit more, but as a player this would tend to irritate me, yes. If the players have made it pretty clear that they're not interested in desert shenanigans, why is the GM bringing things back to the desert?
It's not as if, at the beginning of creation, it was deemed that this particular RPG group
must play out a desert scenario. The GM, in your example, has control over backstory - so why not put forward a backstory that speaks to the players' interests rather than contradicts them?
The worst example of the sort of GMing you're describing (and apparently endorsing) that I have personally experienced involved a 2nd ed AD&D game 15 or so years ago. The group was fairly large (6 or 7 players) and had well-established characters with a lot of intraparty relationships based on various forms of connection to the gameworld, including a prophecy that the GM was in control of and that seemed to be the focus of the game.
Around 8th or 9th level the GM, without any foreshadowing within the fiction, nor any out-of-game discussion, moved the whole game 100 years into the future, via some sort of temporal teleport. Suddenly all the relationships that the players had built up between their PCs and the gameworld, and all the work we had done trying to make sense of the prophecy in relation to our PCs and the gameworld and those relationships, was invalidated.
I left the game not long after, and I don't believe that it lasted much longer after that. In effect, the GM killed it off. My impression is that he had lost his sense of control over his own backstory, but wasn't prepared to follow the players' leads, and so in effect "rebooted" things so he could start with a blank slate.
The GM shifting a game in which the players are clearly invested in City B, to one where the desert that the players clearly are not interested in becomes the main focus, seems to me to be a (perhaps lesser) version of the same bad GMing.
Of course, it could play out differently. Perhaps the players don't really care about City B, but rather about something in City B - say Item X. A good GM might be able to adjudicate the City B action, and let the players learn that Item X is really to be found in the desert, in a way that leads the players to become invested in the desert because it is the receptacle of Item X. Being able to pitch the players' concerns back to them in unexpected ways is a key GM skill. But it takes more than simply laying a trail of breacrumbs (to borrow [MENTION=22779]Hussar[/MENTION]'s phrase).
Let’s flesh it out, because right now, my answer is “it depends”. Did I ask if the player wanted to examine the possible purchases and make some Handle Animal checks? If he responded with “I want a horse, I want it immediately and I don’t want to screw around with your lame NPC characterizations and minutia rolls.”, then I get the sense the PC is rushing the deal and having him buy a lame horse may be a reasonable result.
Once again you are conflating "effort at the table" with "effort in the gameworld". That's one way to play, but not the only way.
It also depends on the character – if he’s a Ranger with the Horse Lord archetype and a +15 Handle Animal check, it seems unlikely he would fail to notice the horse was lame under most circumstances.
Now this is interesting!
Does the player with the Horse Lord Ranger have to spend
more time at the table doing horse-y stuff to get the benefits? Or is one benefit of being a Horse Lord Ranger that you get good horses without having to spend time at the table? I think different groups have different views.
Hussar has been prettly clear that, by summoning the centipede, he's trying to get the benefits of a desert crossing (ie being in City B) with less rather than more table time. I say, in those circumstances, give it to him! It's not as if there are no complications to throw at the players that they are interested in, such that we have to fill our play time resolving situations that they're not interested in!