Sorry, but that's not true.
A year from now, newer applications will only feature the newer design. Developers will also stop supporting the older branch of their software that featured the older design.
For reference, many developers who were committed to preserving Snow Leopard compatibility have since stopped doing so - how many are going to support two different user interfaces?
I get what you're saying. But no one's forcing me to upgrade the applications either. I can continue using whatever is supported on Mavericks if I choose to stay behind.
To clarify my thoughts a bit: of course I do not expect to stay on Mavericks forever. I'll stay for as long as it is sensible for me – that is, until I decide it's time to move on, until I get a new Mac (this Early 2008 MacBook Pro needs to be replaced with a faster, more capable machine at some point) or absolutely need to use that new version of an app that no longer supports Mavericks.