Here's the most important thing it contains for developers:
Most people (more than half) who use a Windows Phone use a lower spec device.
However, in my experience:
Most developers who use a Windows Phone have a higher spec device.
And, most developers only have one device
There's a disparity here. Does it matter that developers are using devices that are, potentially, very different from the ones their users are using? I think it does.
To ensure an app works well on a lower spec device (or one with a smaller screen - if you have one with a large screen) it's important to test on such a device.
The emulators are good but real devices are better.
If you don't have a low spec device, find someone who does and ask them to let you borrow it.
Alternatively, and fortunately, the lower spec devices are cheap. If you're building apps to make money then it's a small investment to buy one.
Very few developers have access to a wide range of devices. A table like can be seen below is not the norm. Don't be disheartened though. For the most part, as a developer, you don't need this many devices to test on.
My suggestion is that if you're getting devices for testing and you can only afford two, you should get one with the highest spec and one with the lowest spec available. A Lumia 930 and a 520 are probably the most appropriate options right now. If you can get more than this, then I'd consider something with a larger screen, like the 1320 or 1520.
How many devices do you test on?