I think the guideline applies to apps with user-generated content. Now, I'm sure you can come up with an argument about why this still applies to Safari... but

I think the guideline applies to apps with user-generated content. Now, I'm sure you can come up with an argument about why this still applies to Safari... but it's also easy to come up with an argument about why it does not. Certainly, the relationship between the content and the app is much more tenuous for Safari -- where the content is everything published on the web by anyone -- and the Tumblr app, where the objectionable content is hosted by and for the Tumblr app. In the end, you can argue Apple should have drawn the line about responsibility for content in a different place, but clearly a reasonable line can be drawn that allows Safari but doesn't allow Tumblr (with a broken child-porn filter).