ISPs can see a lot, but it does have limits. As long as we're using SSL (and I suppose, assuming it hasn't been cracked), the ISP really only knows what domains I'm visiting. So they might know that I'm going to WebMD, but they don't necessarily know that I'm reading up on treatment options for nose fungus. They also don't necessarily know exactly which member of my household is going to that website, nor can they link it up with any browsing I do from the coffee shop.

Browser-based tracking, on the other hand, can see just about everything, because it's looking at the state of the data after it's been decrypted. And it can, with a reasonable degree of confidence, individually identify people, even when more than one person shares an internet connection, and even when one person uses more than one device or connects to the Internet from more than one location. The higher fidelity of that signal does imply that it's a greater privacy threat.