The accusative of стол is стол. https://en.wiktionary.org/wiki/%D1%81%D1%82%D0%BE%D0%BB
It's not terribly common to be telling someone else what they see/hear/think/etc. anyway, so I wouldn't say it's that uncommon to use Present Progressive, at least for see/hear.
A case where it's appropriate and relatively common is in explanation or narration:
"You are seeing the effects of inflation."
"You are hearing the call of the African swallow."
"You are thinking you shouldn't have done that." (Far less common, even when rephrased as a quotation: "You are thinking, 'I shouldn't have done that.'")
"Knowing" is another matter. I can't think of an example where "you are knowing" is likely. The exercises could definitely do with being lenient on seeing/hearing, though.
It actually is uncommon, because both "see" and "hear" are non- action or state verbs, like "know" the majority of the time.
In the examples you provide you are refering to situations where is clear what action the person is taking
"You are seeing the effects of inflation" either the subject is looking at a graph or something, making "see" active
The person has asked for an explanation why something is expensive, making "see" abstract.
In it's regular context see is decribing a state, a experience you have and the process cannot be observed or measured externally.
Imagine you are explaining your room in thefirst person - i see my bed, i see my chair, i can see that it's raining outside, etc.
Same principle works here.
As for your "hear" example, i'd say you used an unusual formulation as the present simple would be more suitable in most cases for the same reasons as above.