Because 559 and 622 isn't enough..
Its a bit decision these days choosing the wheel size of your bike and its not to be taken light-heartedly. Although more and more people are making these different parts, it can still be difficult to find a shop when you are in the middle of nowhere that supports the 'new' sizes. Of course there have been dabbles with the non 26" wheels in the past and some of them are only just becoming popular. 29ers are a prime example. They have come and gone and now they are back to stay. The great thing about all this is that you have the choice. I cant see the 650B craze kicking off properly for another couple of years but its coming...
This is a great illustration from http://www.justridingalong.com
There is also an interesting timeline and more information here:
For more information on wheel sizes or if you are looking to upgrade you need to come and have a chat with us in store. We can talk you through the different options and we are here to help. Feel free to call also, on 01926 430211