Inspired by an exchange on a recent question, I wanted to know whether there is any good reason to develop Windows Phone 7 applications that target pre-Mango models, i.e. by creating applications that target the 7.0 APIs rather than the more recent 7.1 APIs.
My impression was that because the Mango update has now been fully rolled-out, there is very little reason why anyone would have a phone with a pre-Mango OS. My guess is anyone with a pre-Mango phone probably never connects it to their computer and probably does not download applications.
Are there any good statistics on OS version demographics that can inform this decision?
I know from the analytics of my apps that there are still people out there using pre-Mango versions of Windows Phone, but as you point out, they are unlikely to be connecting their phone to their PC to perform updates or even update apps they've already downloaded (my wife for example would still be on the original shipped version if I hadn't updated her phone myself!).
With that in mind, personally, I don't see the point in creating applications now that target pre-Mango versions of the operating system. The return is highly unlikely to warrant the effort.
There isn't much of a reason to target pre-Mango as opposed to Mango as the upgrade is available to all models of phone currently, and for free.
It is worth keeping on the latest SDK for no other reason than there is no reason not to... lol, made sense in my head. Things like performance improvements, bug fixes, new features etc are all reasons to keep up with the latest, as you are likely aware.
The only reason I would target an older SDK is if a particular version of the phone OS was not available to a certain piece of hardware for any reason.
Then again, if you can make your app with the lowest common SDK, why not - it will in theory only increase your user base as backwards compatibility is enforced, over choosing a newer and not-completely-rolled-out version. You just personally suffer the older APIs and miss out on new features. However, I see this counter-point as a largely academic argument and adds little weight to the choice of older versions.
Save yourself the headache, go with the new stuff. Anyone actively using their phone enough to also use your app is likely hot on updates.
I don't do 7.0-specific programming any more since the roll out of Mango is now available pretty much everywhere I'm interesting in deploying apps. This question will rear it's head again when vNext is released (with potentially updated hardware requirements / sensors, etc), but for now I can't see much reason to target the old version.
