I expect v7.1 will not break v7.0 . I expect that v8.0 can break v7.0. Major version numbers are for exactly that reason, breaking changes. So typically, if you upgrade from one version to another you can accept that things may break. People should read the change log before upgrading. Same as v1.0 of an API can completely fuck apps coded against v0.9.
I'm talking the trend of V7.1 supported, 7.0 not. With no protcol changes, as are in this example, a chat client.
This isn't really in direct response to your OP, just version numbering in general, and stuff like Windows is a bit different, where Microsoft would go bankrupt if an upgrade from windows 8.1 to window 10 meant you had to reinstall all your data and your software working on 8.1 doesn't work on 10. MS are a definite exception though, with their diligence in maintaing backwards compatibility.
Considering you can still run like VB6 apps on Windows 10 x64 ... yes!
That's with a bit of finicking with some OCX and DLL but it works.