[parasubvert]

And I can guarantee that the vast majority of long-lasting, maintainable applications out there (10+ years) are are tightly coupled to a framework somewhere.

There is a mindset out there that all coupling is bad. Uncle Bob's point of view that coupling to a specific framework is unwise, is one long held by OO design purists.

I'd rather prefer it thought that tight coupling is a tradeoff. You are trading productivity today for future migration risk.

If you know your app is a Rails app, and will always be a Rails app, then there's little reason to decouple. The question, is do you really know, or how reliable are your guesses?