Given an existing choice between Unix-based IOS (on the iPhone) or the Linux-based Android system; why would anyone even think of buying a smartphone that is Windows-based? It's bad enough that so many people are stuck with having to use Windows on their desktop systems; I can't imagine anyone wanting it on their smartphone or tablet as well.
As someone who has used all 3 systems... Windows Phone 8 is by far the easiest to use and that is what ultimately made iOS as big as it is. People think that iOS is easy to use (I disagree somewhat with that and it seems the new iOS guy agrees with me) and Android is not, so people who are afraid of technology choose iOS... well Windows Phone 8 is even easier than iOS. Also of the 3, my low powered low priced Nokia 620 is by far the smoothest of all the OS I have tried... Windows Phone 8 is freaking smooth to use.. highly responsive... even more than iOS and the iPhone 5.
Android is much more customizable than Windows Phone and iOS, but Windows Phone is more customizable than iOS as well. Integration between apps is also superior to iOS, but not as much as Android... but Microsoft has promised even more in future updates... something Apple has not.
iOS has most apps, followed closely by Android, but the fastest growing store is Windows Phone store.. and almost all the big apps are there.. only Instagram (official) is lacking as far as I can see.. but that should be in the works.
The reason I choose my Nokia 620 is the following.
1) I always choose to buy my phone fully, hence price matters. Blowing 650 Euros on an iPhone or 500 on an Samsung Galaxy S3... not an option... and yes I could afford it, but I refuse to pay that much for any computer device!
2) I wanted a smartphone with a GPS system, (preferably Google Maps), music player and the ability to install basic apps like Twitter/Facebook and fitness apps.
3) I wanted an Android phone but the cheap Android phones are crap and run Android 2.3 and not 4.1+ (aka Jelly Bean). That is a deal breaker for me after working with Jelly Bean for a year... you just cant go back as they say.
4) I then checked what phones are listed by the various review sites as the best cheap phone and they almost universally choose the Nokia 620. Review after review praised the 620 for its quality vs price and what you get... and I have to agree with them.
As a bonus for choosing my Nokia, I got a free music service like Pandora, great maps and other bundled software... you might say bloatware, but I say extra free software in this case.
I do miss my Google Maps, but there is an app for that on Windows Phone (non offline sadly) and chances are Google will make a native app as well.. but saying that since I have a Nokia, I have a full offline mapping system using maps that most GPS software companies use (since it is owned by Nokia). I also miss the massive amount of integration Android has with its apps (like sharing and such) but I can live without that since my phone is not my primary mobile entertainment system... my Nexus 7 is.
I do have one annoying thing with the Nokia 620... only one setting for volume.. so you cant have your music player volume at 50% and your ringer at 100%.. hopefully they will change that soon with an update as I know it is a complaint people have.
In the end I paid 220 euros for my new smartphone... about 1/2 of a top end Android and 1/4 of the iPhone... and I get just as smooth phone with all the important apps and a good camera (720p recording with all the bells and whistles usually seen on high end phones).
Not to mention.. I got Office on my phone so I have native access to my documents and spreadsheets on my phone... cant do that on Android or iOS (note I said native access).