Nikon doesn't make a lot of lenses people would like to see made, simply because 80 percent or more of cameras sold are D40-D60-D3000 class bodies, and the vast majority of sales are to beginners, hobbyists, and advanced amateurs with modest needs and modest budgets, and a decided preference for smaller, lighter, and lower cost lenses. A 55-200mm f/2.8 would be a popular pro lens I think,and the difference between 50mm and 70mm on DX is significantly wider. I myself a few years ago, blogged about the need for a 50-250mm, fast lens for sports/news use, before Nikon had any full frame camera options.
Pentax makes a neat 60mm-250mm f/4 constant aperture zoom lens in its premium DA* line (pronounced D-A star)
smc PENTAX DA Star 60-250mm F4 ED (IF) SDM - Official PENTAX Imaging Web Site
which for a 1.5x camera body makes a lot of sense.
The current 55-200 lenses are small, light, and very easy to carry. An f/2.8 model would probably cost $2,500 or so,and there probably really isn't as much demand for that lens as for other lenses that sell in big, big numbers.
it'd be possible to make a good 55-200. I wish Nikon would make a quality 35-135mm f/2.8 or a 35-150mm f/2.8. I own an older 50-135mm f/3.5 Nikon zoom which is wonderful lens on 1.5x, simply due to the wider field of view at 50mm as opposed to 70mm on my 70-200. With high-quality newer sensors and better and better high ISO capabilities, an f/3.5 max aperture would be somewhat equivalent to an f/2.8 lens from five years ago, when maximum ISO before severe loss of image quality was limited to the 1250 to 1600 range. And that's another reason slower aperture zooms are possible today; today's ISO 400 from a top camera is about as grainy as Kodachrome 64 used to be. Wider aperture lenses are not quite as imperative today as they were even five years ago; the newest Nikons can shoot good-to-usable images at ISO 3200 and 6400,and now there are 25,000-104,000 ISO settings hitting the market.
A 55-200 consumer lens at $250 versus a $2,500 model is a simple economic decision for Nikon. Just not enough demand for the big gun.