It's not that Apple products have got any worse, although they do continually shoot themselves in the foot with cock ups like the iPhone4 losing signal when you answered it, the new useless mapping software and the new connector making all your expensive add ons redundant.
The real issue is that the competition has got so much better and now their products lead the way. That is why Samsungs market share climbed 12% in Q4 and Apple slumped 20%. You can only charge premium prices when you have the premium product and Samsung have wrestled that from Apple. Building on that Android allows other businesses to easily compete and Nokia/Microsoft are starting to gain traction.
Apple are still stunned by the death of Steve Jobs and are shackled by some of his more dubious points such as nobody wants big screen phone (the market shows otherwise) or a 7" tablet (the market again proves him wrong). Even worse new technology is all about moving on, improving the look and feel something that Microsoft have got better with as they move Windows forward. Unfortunately Apples iOS is stuck in a five year time warp with the same look and feel.
All of the above will slow Apples growth in a rapidly accelerating market.