It is kind of funny how responsive design has become perceived as a silver bullet for web design. There are still situations where a traditional m.domain.com approach is better.

Responsive is great if your site is mainly concerned with serving up content, like a news site or blog. But if your mobile users have significantly different use cases than your desktop users (as is sometimes the case with applications), it may make sense to serve up a separate app entirely.

Not to mention that it's still really hard to optimize responsive to the point where it performs as well on mobile as m.domain.com sites