Warwick's are great for metal because they can be aggressive and punchy basses, and it seems that the Warwick artist roster is fairly laden with metal guys. Maybe it's a geographical thing (made in Germany, closer to all the awesome European bands). It's hard to say why players from other genres aren't better represented.
But their basses are pretty versatile - the Streamer and Corvette $$ have to be two of the most versatile basses on the market these day. Not to mention all the little features you find on Warwick's that you don't get elsewhere; cool woods, brass frets, 2-piece 3D bridge, Just-A-Nut, etc.
The Thumb is probably the 'flagship' Warwick bass because it is so unique in the bass world and no one makes a bass remotely like it. All Warwick's are growly and punchy, and the Thumb is particularly so (it's hard to hide this bass in a mix). The Streamer Stage II is the closest alternative 'flagship', I'd say.
I have a Fender (and a Squier) Precision and a Warwick Corvette 6. With those two, you can basically cover any style or sound thrown at you.
For a good example of Warwick, check out Stuart Zender on Jamiroquai's Cosmic Girl, or anything of their's pre-1998: