The servers in this example were configured to be asynchronous. The clients were not. You may still be using asynchronous clients in your code but James's argument is that Java developers don't tend to do this because it requires a lot of boilerplate. Scala developers do this because it's very low syntatic overhead and frameworks+libraries embrace it.
Developers who don't do something that would give them incredible performance and resilience because "it requires a lot of boilerplate" are bad developers.
Not necessarily, more code means more maintenance which translates to more cost. Adding new features requires more research, more work, more time, more cost. Fixing anything requiring a patch after going production with a new feature would likely be more expensive. Testing tools have to be verified to work with the additional code. This all increases costs which might be OK for some organizations and not so much for others.
That's a different argument though than just "it's more code so I won't do it". If we are discussing performance then the assumption is you have a performance problem you need to fix.
