I use PA as a way to always "bring my own computer with me", regardless of what computer I'm sitting in front of. As long as I have my phone, I can just jack it in and have all my software neatly available.
Now, to have "my computer" with me, it would be nice to also be able to save web links in PA, preferably in the form of some kind of (multi-level) menu, much like the one that pops up when you click Apps, probably best located among the various document type buttons. Clicking in the menu would launch a browser with the URL.
That is what bookmarks in a portable browser are for. I can't see the need to duplicate in the Platform functionality that is available in at least 5 different official apps.
But that's the problem. I'd need to duplicate it in several official applications, as I use several browsers. Opera for most sites, Chrome for a few problem sites, Firefox for use with TOR, sometimes Iron if I'm feeling suspicious, all of them plus Links and Lynx for testing.
That's why it would be neat to have them in one place.
Your argument is like saying that there is no need for PA to handle a documents folder, as each application can decide by itself where it wants to save its data.
It's useful to have a centralized data storage, regardless of data type, especially in this type of "on the road" situation (even though I'm more and more replacing ordinary installations with PA, even on my own computers, simply because it's so much easier to install and upgrade, just a simple batch copy from a working setup and it's done).
I can't rightly say for Opera as I use it for testing purposes only, but you can sync bookmarks across Firefox, Chrome & Iron with an extension called X-Marks.