No one wants to have a huge clunky phone
Have you seen pretty much every flagship Android phone currently in production? "Huge & Clunky" is the new black. 4.5"? Why not 5.5"? Or better yet, 6.5"? Hell, let's carry a small television in our pockets!
Like others have said, WP will stay in the game because Microsoft can subsidize it's survival for as long as it chooses to. I just hope they make the most out of it and turn it into another Xbox... The OS is fantastic but it does need some buildout before it becomes a true contender.
RIM has a great chance to take over at #3 though. I'm amazed at how many corporate IT departments still insist on old BBs as the corporate phone (primarily for the security component). With RIM's new "work/home profiles" functionality, I can see a lot of people jumping to the Z10. I sat in a meeting with a new healthcare client a couple of weeks ago, and I was amazed at how many people carried both a BB and an iPhone (probably 25-30 people in the room). If the "home" profile can do 80-90% of what an iPhone does, why carry two phones?
Of course, BB10 MUST succeed... If it doesn't, RIM is finished.
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BB10 will merely match features that iOS and Android have had for years now.
It's funny, Android fanboys have been saying this about iOS (vs. Android) for years now... and yet, iOS is still doing just fine.