I don't think of 28-200 as a superzoom, it's "only" 7.14x!
I am no expert, but I will try to answer from what I know:
1. DSLR lens 'superzooms' are usually lower than Superzooms.
2. The FZ50 may have a 12x zoom, but if its wide angle is 35mm (suppose so, I am not sure!) than it means the lens is a 35-420mm lens. Now, if you have a 200mm DSLR lens, Canon will multiply its focal length by 1.6, Nikon by 1.5, and Milonta by 2. So, your lens will be equivalent to a 320mm lens for Canon, 300mm lens for Nikon and a 400mm lens for Milonta! (that one's pretty close!)
3. Don't confuse the mm and X. X is the ratio of the Telephoto to the Wide angle. So, if you have a 50-100mm lens, it is 2X, and if you have a 100-200mm lens, it is still 2X, but it will take you twice as close! So, if you have a camera with a 25mm wide angle with 10X zoom and a 35mm wide angle with a 10X zoom, the Xes may be same, but the 35mm one will take you 1.4 times closer at max telephoto!
Hope this helps,