as salaamu alaikum,
windows mobile devices have a whole lot of available applications and sync well with windows productivity applications, but are not always the most stable. other platforms (symbian, palm, etc.) may be more stable, but not always ideal for demanding business users. so RIM created the blackberry platform for just that market. business users need very reliable, bullet-proof devices that work well for everyday productivity-intensive use.
so theoretically, the blackberry platform comes from this tried-and-true business pedigree, and the pearl/curve series are supposed to be specialized versions of the blackberry platform geared towards consumer users. more stability but in a user-friendly package.
i personally think that so far, they still feel more like business-oriented devices. hopefully the newer models will change that.
meraj