Cause motorolas use a crappier UI. SEEM editing on a Motorola is 1. only on their non-smartphones and 2. more open, and thus slower and more susceptible to Carrier modding.
Nokia's smartphones use Symbian S60, which is actually not technically a Nokia product at all. Symbian is a separate company (though Nokia owns a majority share, Samsung, SE, LG, and other manufacturers have a stake, as well).
Symbian is also very secure, inherently. It's the most-used Smartphone OS in the world, something like 78 percent, I think. The newest version (9.1, which your E62 uses) is even more secure than previous versions because they require apps to be "Symbian Signed" which means they're tested for compatibility, stability, and security.
Symbian firmwares aren't hackable.