The other browsers may have more options that those offered by Safari. For example, Atomic Web Browser and iCab Mobile offer you the opportunity to ID your browser as other than mobile Safari, which helps in NOT getting mobile web sites. Also, iCab Mobile also offers you the chance to upload files to the web.
Many of the alternate browsers let you customize colors, full screen ability or increase/decrease fonts. In many ways, alternate browsers offer a more fuller browsing experience. For example, I can use Atomic Web Browser to increase the font in the web view. This is a true increase, as in the text wraps, versus a simple zoom as offered by Safari.
The point is that if you want a bit more out of a browser than what is offered by Safari, there are many out there. It is up to the user/buyer to determine what features they want that are not available in Safari.
Marilyn