I find that this is such a superior approach for certain websites. If a site has a large number of secondary pages designed around totally different content, the "only touch the stylesheet" seems to lead to despair.

I've seen people crap out things like #aboutPage #mainContent p:nth-child(2) div button {styles go here} ... because they follow the "separation" concept blindly. And then, you know, a paragraph gets added in later. Made up example but you get the point.