Not mentioned here: pattern matching. It certainly goes a long way to ensure all cases are being handled, since the compiler lets you know when your patterns are non-exhaustive.
"Yes, you can write more concise code; yes, you have a more advanced type system; yes, you can pattern match. There are hundreds of other reasons that Scala makes a great language. When a language can offer me constructs to write more correct code, I'll always be willing to deal with the learning curve."
I think the point was that these are the things that he thinks are of more value to developers than the other good things that Scala offers.
Pattern matching offers mainly correctness and conciseness, maybe the correctness part should have been emphasized more.