As every Analyst has said a Tablets success is based on 3rd Party Developers, I don't know much about the Blackberry App Ecosystem, but there are so many devices that developing apps is difficult for everyone who owns a blackberry, all with different sizes, input types etc.
Apple has made the iTouch and iPhone almost the same, as even Apple has said, the iTouch is an iPhone without the Phone. The iPad is as many put it a big iTouch, making it easier to port apps to the iPad, all you have to do is click a few buttons, change some code and BAM, you have an iPad app ported over from iPhone.