It's true, responsive / adaptive front ends are already here, many large organizations are investing in a "one platform" to rule them all because the technology is more supported now and what may cost more to build initially will save them in the long run because they aren't supporting a bunch of different stack setups. One front end to rule them all.
In one of my themes I demonstrate how RWD can work for mobile, tablet and desktop all under one front end using CSS & media queries. (shameless plug)
https://www.adultwordpressthemes.com/product.php?id=50