Yes, me and someone else on CS were saying the other day, we now have three lenses that cover 24mm ;p
More lenses are annoying though because it's either more to carry around or more that you can't carry around.
I must admit to reaching for my primes less and less these days. I took my 85 instead of the 70-200 for a shoot on Monday, something I've rarely if ever done before, and regretted it even before I got the camera out of the bag.
1. f-stop/speed -- I own a 18-200 and also a 50.. cos 50 is f1.8 and can shoot in minimal light and can bokeh well. My 10-20 can do 18mm also, but I use my 18-200 for it because on my 18-200 i can hit it at f3.5, but on the 10-20 i can only do it at ard f5.6
2. Image Quality -- Primes, besides being faster, are also (arguably) sharper, and give better colour vibrancy and "pop"
3. Other factors -- like nightmare said-- sometimes its size, or what you think you're going to shoot. If I'm shooting an event indoors, I might want to use a 18-50 f2.8 instead of a 18-200 f3.5-5.6 which i might use for travelling. I would give up the ability to get super closeups at the 200mm end, and trade it for better IQ for the more general shots that the client might have asked for. Even if it's not a prime, different lenses have different uses.
i carry a Sigma 12-24mm F4.5-5.6, but i also carry a 24mm prime becase the later provides a larger aperture for other creative options, apart from better IQ. the 12-24 is a very convenient wide zoom for me
I used to tell many people .. lenses are made for specific purposes. There is no magic lens that cover the entire range and does all kind of regular stuffs such as landscape, portraits, macro.
Like many of us, I would also love to have that magic lens ;p
Technically the requirement for landscape lens is different than the portraits, in some way opposite. So technically you can not have a lens that is equally good at landscape and portraits. This is just an example and there are so many this kind of contradictory requirements from your lens.
So, it's not the range, it's the specific purpose the lens is build is more important. Technically, fixed lens (prime) are the most fine tuned. As the range increases, it is hard to maintain quality throughout the entire range and hence we talk about sweet spot of lenses (along with f value).
It's not about range, say 10-400mm, it's all about specific purpose of the lens. You use different lens for different purposes.