That survey discovered that people with devices with larger screens download more data.
"[with] each additional square inch of screen ... 288 MB more data [was] downloaded per month,"What does this survey mean to Windows Phone developers?
The survey is based on Android users so there's an argument that it might not directly apply. I don't see a big issue with assuming that the results of the survey can be universally applied. Anyway, it's not as if such a survey is really possible of Windows Phone users just now as the range of devices currently available would prevent such a survey being possible.
Why might this be the case?
Why would people use more data (over Wi-Fi) with larger screen devices?
I can imagine a couple of reasons:
1. Apps (and websites) may be downloading larger assets (images) on larger devices to prevent the best looking content to the user. If this was really the case then I'd expect increased data usage not only on Wi-Fi though.
2. People usage larger devices differently to smaller ones. We "know" this. But sometimes it's easy to forget. Different sized devices are used by different people, in different ways and at different times. Larger, handheld devices are used more for consumption than a "phone" traditionally is.
Why should Windows Phone developers care?
Nokia's new Lumia 1320 and 1520 devices will be available shortly. They are considerably larger than the Windows Phone devices currently available and so are likely to be used in slightly different ways and the above survey results may apply.
What can we do with this information?
Regardless of personal opinions about so called "phablet" devices it's worth remembering that some people like them and that they may use them differently to traditional phone size devices.
It might be tempting to assume that more data usage means more apps are used. I don't think this is the case.
I'd expect that apps are rather used for longer as is the pattern for larger tablets compared to phones.
If you're a developer working on a Windows Phone app that is focused on data consumption then the above survey should help confirm to you that making sure the app can provide the best experience on ALL devices is in your interest and that of your users.