when must I use "of" to link two nouns

[emsr2d2]

Is it wrong?
I got it from several English courses on the net, I have read the following on: dictionary.cambridge.org

"When we don’t use ’s​

We don’t use ’s when the noun is not a person, animal, country, organisation, etc., or when the noun phrase is very long ..."

Their use of "etc" is really unhelpful. How are you supposed to know what's included in that "etc"?
The following example sentences are correct and natural and don't follow your "rule".

The palace's turret is starting to crumble.
The car's bonnet is still hot so the car was clearly driven recently.
The suitcase's wheels are very squeaky.

 

[semcem]

The following example sentences are correct and natural and don't follow your "rule".
.

It's not my rule, I'm not an native English speaker; as I said, I found this in many English courses on the net. Perhaps it's not 100 % correct. However, it is accepted that the use of "of" in such cases is more recommended.

 

[Rover_KE]

The following example sentences are correct and natural and don't follow your "rule".

The palace's turret is starting to crumble.
The car's bonnet is still hot so the car was clearly driven recently.
The suitcase's wheels are very squeaky.

Also:

Our hotel is only a stone's throw from the beach but an hour's bus ride from the zoo.
Edmond Halley predicted the comet's return in 76 years.
Tomorrow's weather looks like being much better than today's.
The shop's opening hours are 7am to 11pm.

... plus countless others. The so-called 'rule' is only useful as a vague suggestion with thousands of exceptions.