Keeping the Existing Codex for 11th - what does that actually mean?

Considering 40K codices can be completely rewritten (more or less) and expanded after the fact, does the fact everyone gets to "keep their codex" actually mean anything? This isn't like previous non-reindex versions where the book stayed the same between editions.

I'm fully expecting huge swathes of points and army rules changes when 11 drops. To the point where you're not really keeping anything. Plus everyone is getting new and reworked startegems.

Feels more like we're just told that we don't have to pay for another book.

Thoughts?