Because this is what it’s like trying to browse using the currently available ultra-portable computers (with 10″ screen):

The area in white is the “active” area of Google Reader, ie the bit that actually contains the content and scrolls– at 248 pixels high it comprises less than half the total screen, which is only 600 pixels to begin with. This is just ridiculous. It’s a total fucking waste of pixels.
Apple’s tablet (which I doubt will be called the iSlate because it sounds crummy and a bit like “isolate”… and at some point they’re bound to drop the “i” from their product line) will probably be used mostly in portrait orientation, immediately addressing the problem of the unreadable short and wide page. It will probably be higher resolution so text will be crisper (I’m guessing 1440 x 960, which would be lovely and would keep the 3:2 aspect of the iPod Touch and iPhone with dimensions scaled by a factor of 3). It will have a clean and unobtrusive UI minimizing the amount of unnecessary junk onscreen and reclaiming at least half of the real estate that standard desktop GUIs currently waste.
Even though I bought this junkbook (HP mini 110-1197TU) today*, I can’t wait for it to be rendered useless by a soon-to-be-announced reorientable multi-touch expensive thingamabob. As a friend pointed out recently, the greatest feature on a netbook is the “stand” – ie the fact that the keyboard part acts as a stable base. If Apple can solve this too, eg with an unobtrusive foldout for standing the thing up on its own (like a picture frame) then they will truly deserve their success.
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* for traveling with… I just wanted something small I can type and watch movies on, and the iPod Touch is a little too small and proprietary about its media support.