I think you're being a bit generous.
For starters I wouldn't say that they've perfected the form factor of the iPhone at all. The current shape looks odd because it was dictated by the competing demands of a larger screen (to compete in a market where larger screens are more popular) and the need to maintain compatibility with docks and accessories designed for a smaller phone. The UI isn't being refined, it's being updated to eliminate the awful skeumorphism that served them well 6 years ago and catch up with the trend for a more authentic digital UI that Microsoft started with Windows Phone.
The common thread in all of this is that Apple are playing catch-up but are still burdened by the myth they created of themselves as an innovative, revolutionary company that sets rather than follows trends. They have boring, dated products and they're attempts at updates seem boring because they don't live up to the promise.
I'm not saying the iPhone is perfect, what I mean is that they have refined their form factor for the current iPhone to its completion. Basically the form factor is taking a back seat while they refine or catch up the Software. Very rarely has Apple over hauled the software and hardware at the same time. What most fail to understand is that Apple doesn't innovate in the traditional sense. They very rarely bring an idea or product to market that hasn't already been done. They innovate by refining what already existing and make a really good presentation of it.
Also another thing to add if you look at the industry as a whole right now, there really isn't anything majorly new in the mobile market, something that Apple can capitalize on, everyone seems to focusing on UI/Software at the moment. Tablets were the last big push, but nothing huge since then.