It’s more to do with resources and costs, why spend money supporting a 10 year old OS that could hold back future developments and movement into newer technology that can utilise functions on a hardware level? This is a stake in the ground for Steinberg and a heads-up for Win 7/8 users of their plans.
I’m pretty sure that they will respond to any application breaking bugs in win 7 ‘where they can’ as part of goodwill, but they won’t be recommending or supporting users in an official capacity. As they move to newer API’s, incompatibly with older OS’s are sure to arise - i think that’s the point -steve- is making, but until 10.5 releases they won’t fully know. Many API’s do have compatibility options, but it gets messy when you start adjusting builds for obsolete OS’s.
Mac users went through the same process with the Metal API, applications that utilised it had to have a GPU that supported it… So Apple made it a requirement for their OS, 10 Years of Win 7, really is something Apple users would love - Logic for example requres MacOS High Sierra (2017). And Cubase you have to be running MacOS Sierra (2016). Compare that to supporting an OS which goes back to 2009 and the multitude of issues that ‘could’ show up when moving to newer frameworks - well, they’d have to go in and test it all to tell you ‘what’ doesn’t work.
But what’s key in the question you’ve asked is that it’s only relevant in the final build to give you a definitive answer. In it’s current state, C10.5 may not even start in Win 7, or is very buggy generally. But as Steinberg products are cross platform it will be their own Frameworks which may be tweaked globally to allow Win 7 users to run future versions - really depends on the amount of work i guess. So it’s very complicated for them to tell you ‘what’ works or doesn’t.