You really have to think of Blackberry in a longer context:
Blackberry was the first device to make serious market inroads with text-oriented pagers (yes, pagers), when I worked on the 2000 presidential campaign that's what all the politicians and CEOs had. It quickly supplanted Palm Pilots as the "prestige" executive device.
They then added a phone to it so it became even more useful and a sign of having an important job if you had a Blackberry phone.
Lawyers, certain executives and other who actually do need access to email 24/7 really took to Blackberries because having a full QWERTY keyboard made emails a lot easier to punch out. This first-to-mass-market-adoption helped BB because most IT departments first oriented themselves to their mobile network.
Research-in-Motion (RIM is the Canadian maker of Blackberry) then got embroiled in a major patent lawsuit over its proprietary scroll wheel. That's why they suddently shifted to the "pearl" trackball --it wasn't because it was easier, it was because, for at least a year, there seemed to be a chance that RIM would be forbidden from ever using their famous scroll wheel (which I believe was their best control input). This is an important event because I personally thing this hurt Blackberry and set up the easier interface of the iPhone.
Other companies basically tried to emulate the Blackberry until Apple came along.
The iPhone became the most-wanted executive device that most company IT departments were too concerned (or sometimes lazy or irrationally against) to implement. However, when the CEO/major execs or partners want something, IT policies can be "adjusted". The iPhone 3G supposedly allowed for better integration into some major companies so you then saw a rise in iPhone usage among C-level executives.
That massive BlackBerry network outage in 2011 really hurt BB's rep since "reliability" had been a major factor in why departments stuck with them.
In the end, I've had two BBs (scrollwheel for life!) and two iPhones and I prefer the iPhone. I may not type as fast but I type fast and I can handle any business needs and have a nice, simple interface. Android tries to bridge the gap but I know a lot of business folks and lawyers that have been disappointed with various models (all models). I am optimistic for the one that would come out of a completed Google purchase of Motorola, but that won't be for a few years.