I did read it and considered it more of a rhetorical question than a question that expected a factual answer. I mean, who can say except the company why they would consider it something to void the warranty over, and the statement came from the seller and not the builder anyway. So you don't really know that the company would consider it something to void the warranty, only that the seller says it would.
If it was the builder who said that, then it does become a rhetorical question whose answer would be "Because we said so". :)