The biggest obstacle to the competition is the fact that Apple exists and its employees show up for work every day.
I remember the time when people said that about IBM, then they said it about Microsoft. There has always been a dominating company on the market that seemed to make any competition a futile effort.
But strange as it seems, eventually that big name always sank into insignificance. And it usually happened with a technological shift - IBM's mainframe empire got crushed by the PCs, and Microsoft's empire is under the threat of becoming obsolete because of the Internet and Internet-centric companies like Google.
Throughout its existence, Apple has always been a niche player with a lot of hype and press coverage.
The biggest obstacle between Apple and their grand scale success is... Apple. They are a closed shop that does not play well with others and they seriously get the entire third party ecosystem wrong. Someone once said that Apple creates platforms only by accident - while Microsoft intentionally creates platforms and not just simple products. A platform is the foundation for ecosystems.
But Apple does not really like ecosystems around their products. They want to own and control it all by themselves. They don't want to (rule and) share.
And this is why in the phone market Android will eventually win. Just like Windows in the PC market, Android is an open platform and anyone can build a phone around that software.
Sure, we haven't yet seen the end of Windows for mobile devices. But the killer argument for Android are its strong Open Source roots. And ultimately, the developers make or break a platform. Which, by the way, is another area where Apple is currently losing sympathy ever day because of their ridiculous approval process.
Anyway. The iPhone was an important product for many reasons, and it certainly had its moment of glory. However, I don't think that its momentum will last. The competition is not sleeping and especially the Android platform has that element of openness that will attract all those developers that have been pissed off by Apple's closeness and their arbitrary AppStore policies.