First of all, is that market share for the US, or worldwide? Windows Mobile does well in America but its market share is very small indeed elsewhere, that's why it's a distant second to Symbian on a global scale.
Second, I wouldn't say people don't use browsers on Symbians. A lot of people use Symbian phones for browsing the web, now that they have a proper default browser capable of displaying pages almost like a PC, as well as 3G and wi-fi connections capable of loading pages quickly, and high resolution screens capable of displaying most or all of a page on-screen (if you use font and image scaling). It's now good enough for most people to bother with, basically.
Also, many operator and other third party services work through the browser, for example many online stores spawn the browser to allow purchases of music, video, games etc to take place. I recently reviewed the MobiPocket ebook reader, and it had an option for buying ebooks straight onto the phone which worked through the browser. The end user might not necessarily even know they were using the browser as it spawns and closes pretty seamlessly.
And there are many Symbian browsers.
If we're just talking about Symbians that use the S60 user interface, the old default browser is called Services, and is gradually being abandoned. It's no longer default on new models and you can pretty much ignore it, it was written for pre-Symbian dumb phones.
The new browser, which is available on all new Symbian S60 phones, is called the S60 Browser (because it's written for the S60 user interface of the Symbian OS, which is the UI favoured by Nokia). It's also sometimes called the Next Gen browser.
Here's where it gets confusing: the S60 browser is based on Safari and Konqueror, and is intended as an open source project. You can find out more here:
http://opensource.nokia.com/projects/S60browser/
I don't know how you'd classify that, I guess you could say it's a subset of Safari. In fact, if you consider how well S60 smartphones sell, it's possibly the most popular form of Safari as they now outsell the Macintosh I believe.
And don't forget you can actually buy third party browsers for Symbian, for example Opera or Netfront.
And other non-S60 Symbians (such as the UIQ models made by Sony Ericsson and Motorola, or the SOAD Symbian phones made by FOMA in Japan) have their own browsers. S60 is the most popular form of Symbian though worldwide.
