Apple has many revenue streams and while gadgets like the iPhone, iPad and iPod are the ones that form  the crown. It also makes a lot of money through accessories for these gadgets. In addition, many of its third party partners also make a lot of money designing and creating custom accessories for virtually every class of consumers. Hence, it comes as no surprise that the design changes that will be incorporated into the iPhone 5 will render all existing accessories completely useless. The business logic behind this is simple enough: new phone, new accessories, means tons of new revenue for Apple and its partners.

Specifically, we are told that the screen protectors and casings used in the iPhone 4 will become obsolete with regards to the iPhone 5. This means, you cannot re-use your expensive kits on the iPhone 5.
If you are planning to switch to an iPhone 5, I think its best you stop spending money on iPhone 4 accessories because ultimately this will be a waste of money. More importantly, since the hardcore accessories for the iPhone 5 will not be out until after its release, maybe the best option would be to wait for a few more months until it has been properly introduced to the market.  
The news will undoubtedly disappoint those who have spent quite a lot of money on standard iPhone 4 accessories. However, most high-end accessories that are designed for entertainment or functionality such as wireless speaker systems may seamlessly adapt to the new iPhone, which is a good thing.
For users who have spent a lot of money on their accessories but still want to switch immediately to the new iPhone 5, head over to the internet and start selling as soon as possible, while the demand for high-end second hand iPhone 4 accessories is still high. Once the iPhone launch date approaches, second hand accessories may flood the market and reduce prices. Of course, that will mean you will have to be extra careful until you get your hands on the next generation iPhone.