[MaxBarraclough]

That isn't news to me, and it does not undermine my point. Again: A snooping ISP should not be able to tell whether a customer has been looking up an embarrassing medical condition.

Someone going on Wikipedia tells you relatively little. Knowing which specific pages they've been reading, tells you a great deal more.

HTTPS goes a long way to preventing a snooping ISP from telling which page you visited. A truly committed ISP might still be able to infer it from the traffic patterns, but they'll have a much harder time than with plaintext HTTP.