It was already announced in November that RIM was working on a new WebKit-based browser that would be released in 2010. They also filed for another patent in January for technology to boost speed by using proxy servers.
With the popularity of the iPhone and Android devices and for many Blackberry users who are jumping ship for a better web browsing experience, RIM has no choice but to update their browser. The dramatic difference in speeds is something that RIM has to change to remain competitive.
Source: Read Write Web Enterprise