..If Tesla or anyone else is saying that driving on a gravel road is prohibited, then I'd like to trade my car back in and get one that can handle that...
Hopefully, some day Tesla will make an off-road vehicle down the line.
In the mean time, if you decide to get Model S, it's your property so you can do whatever way you see fit after reading its warranty exclusions.
The issue then is: Would Tesla go beyond those legal formality and cover you regardless?
Tesla has bent backward in many cases despite of its more restrictive legal language:
It used to offer free Ranger Service when it clearly posted that would cost a fee.
For years, It was known to tow your car for free to a charging station when the language says it does not cover tow fee for "over-discharged" reason.
And so on...
The warranty exclusions also cite: "racing," "autocross" but yet, that's what owners show what they exactly do on youtube.
It is fine that you would do all those exclusions but just be conscientious that you might need more maintenance than normal and although I have never been heard of Tesla penalizing gravel road, drag racing... owners, keep in mind that just like in this case, Tesla has the right to demand payment for repairs for those damages caused by warranty exclusions.