The limiting factor is reading habits, not browser size. Just because you can design in a landscape orientation doesn't mean you should and wider isn't necessarily better. It's not like magazines are 3 feet across because paper's cheap, right?
I wholly agree (and ended up buying a tablet precisely because I got sick of reading blogs with vast swathes of empty space at the side), but not everything is necessarily better in portrait. I was going to forward the sketchbook link to Mrs Browl, who is redesigning the UX for her firm's browser-based product right now, but then I reflected that that application involves a lot of tabular data and records management and that many uses of the product in a portrait orientation would be terribly frustrating. She is interested in bringing it to tablets, and portrait orientation would be appropriate for many use cases, but not all.
I do think the UX sketchbook is very neat - the squared paper inside the broswer frame is genius. It just seems perverse to only offer a single orientation in 2 different sizes. If it had portrait on one side and landscape on the other I'd buy it in a second (he hinted, in case the makers are reading).
That's a fair point - just because the portrait orientation works for most sites doesn't mean it works for all sites.
So have I got a tip for you, friend. In case your wife hasn't found the right paper for her project yet, the best thing I can think of is to get a giant 11"x17" pad of Edward Tufte's grid paper. Scroll to the bottom of his shop page here:
Not only is it large and easily usable in landscape mode, it uses what he calls a "ghost grid", where the grid is printed with a barely noticeable light ink so that it's visually less dominant and it fades into the background compared to the ink drawings you make on top of it.
I used nothing but Tufte's paper for years and was deliriously happy with it. It was so big that I could use it for all kinds of stuff, whether site flows or detailed UIs, whatever. The only reason I switched away is that not every project needed that much real estate and it's not the easiest thing to carry around. It's like having to tote around a whiteboard.
If she wants something smaller and more portable, there's the dot grid book by Behance:
