Define "needed". Much of the divide between casual vs power users is that the latter will want to use the software in every way possible, many of which you (the developer) won't even be able to imagine.
In fact, those decisions are one of the main reasons why I, as a power user, don't use Chrome or the iPhone - because I crash against the limitations imposed by those choices every day.
Well, for one, I'm a Pentadactyl user just like slowpoke, but also of DownThemAll!, NoScript (from everything I've read, NotScripts is a poor clone - no offense to the developer, as I said, they're limitations of the browser API) and some others.
In the past, I've also used my own extension, that allowed me (and the few hundred other users) to select a piece of text and launch a terminal using it as a command. Absolutely impossible to do in Chrome.
Finally, Tiddlywiki - only usable in Chrome if you install and run a Java program (applet?). Since I don't have Java in my work laptop, no dice.
As for the iPhone, simply installing non-approved apps; old console emulators, for example.
Not the parent, but for Chrome, probably the horribly limited extension API.
I could not even begin to imagine how I would use a browser without Pentadactyl.
Or Tree Style Tabs. Both of which are flat out impossible in Chrome. As are
tons of other extensions.
In fact, those decisions are one of the main reasons why I, as a power user, don't use Chrome or the iPhone - because I crash against the limitations imposed by those choices every day.