While I think Jon made it seem a little easier than in reality, as someone who uses and designs for both mobile/desktop I have to agree that when done right it's not that much more of a time investment - generally ~10% extra on a full design/build project. There's a real argument that in a hackathon 10% extra time isn't worth it, but in the real world where you don't always have 48 hour time limits I've always been in the opinion that the initial time investment is far outweighed by the benefits and the additional cost that you would incur by making it mobile-ready later (which usually requires either rebuilding the frontend templates from scratch or hacking away at the existing codebase in a way that is far less organized/sustainable).
As far as the long standing argument of whether building mobile-first or desktop-first, I honestly think that's up to developer preference so long as the whole team is building with the same mindset. Building responsive, mobile-ready sites/applications isn't free, but a lot of web developers/startups seem to make it out to be much more difficult than it actually is when done consistently and right.
As far as the long standing argument of whether building mobile-first or desktop-first, I honestly think that's up to developer preference so long as the whole team is building with the same mindset. Building responsive, mobile-ready sites/applications isn't free, but a lot of web developers/startups seem to make it out to be much more difficult than it actually is when done consistently and right.