Hi, Andrew, all,
Whenever I read statements like that, "of course tourbillons aren't useful in a wristwatch to improve "accuracy;" or the opposite, "of course it does..." I have to cringe.
It is NOT so nearly cut and dried as that.
In the hairspring vertical position, the benefits of a tourbillon are far greater than in hairspring horizontal position, I think there is little credible dispute about that.
That wristwatches don't need tourbillons because they are in constantly changing positions and thus minimize the benefits of a tourbillon - it would behoove one to consider the percentage of time during a normal day one's watch on one's wrist spends in various positions. For the majority of people, the most likely position (as a percentage of total) tends to be hairspring vertical when worn.
Off-wrist depends on one's habit - to place it flat on its back? or on its side, crown up?
Now if the discussion were a little more considered, e.g., does the tourbillon introduce enough other accuracy impairing variables that it offsets the theoretical advantages to be gaine? That is a whole 'nother discussion.
For conversational shorthand, I can understand the tendency to make simple statements which embody and carry implied points, assuming the other participants in the discussion understand the bundled assumptions.
But in those cases, can we at least throw in a clarifying disclaimer?
TM