I understood that if a WTPV is specified, it's often wrong
because different VS installations have different SDK version
installed. Omitting the WTPV tag makes VS2017 default to
Windows SDK 8.1 which often is also missing, so in any case
people may need to specify the WTPV before building. But some
day in the future a missing WTPV tag will start to default to
the latest installed SDK which sounds reasonable:
https://developercommunity.visualstudio.com/content/problem/140294/windowstargetplatformversion-makes-it-impossible-t.html
Thanks to "dom".
Lasse Collin