It was my first smartphone, I hear a lot of customer complaints about trackball issues, and I didn't want to deal with that. The 9700 was too expensive for me, and the differences between the Bold and the 8520 didn't matter to me for what I needed the device for.
I chose the 8520 for the trackpad, and the fact that it has the functionality I need at this time. When I'm ready for my upgrade two years from now, maybe I'll go for the blackberry with all the bells and whistles, but this is all I need now
That's why I consider it an mid entry level device. It's nice for RIM to make a device that's midlevel and affordable for consumers with some of the newer features, ie the trackpad.