It's not about market dominance. The cell phone market is too large for any one company to dominate. If Apple gains 1% market share, that's something like 10 million iPhones sold.
Not every company has to own the majority of the market in order to be considered successful or profitable. Look at Nintendo if you need another example.
I completey agree, my point is Treos and Blackberry's currently rule the PDA phone market, and being already entrenched as well as specialists in this category, they will be hard to supplant.