Obviously, these things are all about personal preference and what works for one person may not work for another . . . but, personally, I find the 10-inch laptop an idea that looks great on paper but really doesn't come through in practice (and, trust me, I've learned this the hard way). I love the MBA *precisely* because it has a full size keyboard and a big (enough) screen. And I loved my Dell Mini when I bought it -- but after a week it began its hermitic existence in my drawer. The keyboards are just too small (and, sorry, '91 percent full-size' or however they put it just doesn't cut it when you touch type), and the screens too small (oddly, I find the smaller screen of the iPad no problem at all; perhaps because the smaller size works better with a touch interface than with mouse/trackpad.
If a 15-inch MBA meant a bigger battery and a couple more hours of juice, I'd gladly take the extra ounces.
But frankly, instead of petitioning Apple to make a smaller MBA, I feel like petitioning them to keep the MBA at all. I've got a bad vibe that it's not long for this world and that has me very worried, because I think it's really the perfect ultraportable, just big enough and light enough to work.