Disclaimer: I have an "intimate" knowledge about the product.
The WP ecosystem is affected by fragmentation in an Android-like fashion because of how the operating system is rolled out to the devices.
MSFT said that Windows Phone 8.1 will be available to all the WP 8.0 capable devices.. and they meant it. It is 100% true.
However, the most important part of the equation was not mentioned at all: in order to install the 8.1.x version, you need a firmware to support it.
Who develops the firmware? Manufacturers.
That's why all the HTC and Samsung users are still waiting for the 8.1 update and the HTC 8X/8S are not even able to install the latest 8.1 Update 1 Developer Preview.
On top of that, using the developer preview without an adequate firmware, causes dramatic battery drains and performance issues.
Looks like the problem is not who develops the operating system, be it Apple, Google or Microsoft, but who develops the firmware of the phone.
That's why Apple can afford to keep their phones constantly updated.
As Alan Kay said, "people who are really serious about software should make their own hardware"