He might be understanding programming, but from an academic background not from managing large business development projects with issues like compilers, tool chains, on-boarding of new team members, turn over, business pressure to cut corners etc. Scala has very different priorities. The top priority of Scala is "power", language features and the holy grail of marrying FP and OO. The priority of Clojure is solve problems.

Case in point: The lacking Scala API with a high percentage of method calls not described, not explained and rarely any descriptions of classes. Second case in point: In 2013 Scala is still abysmal slow (several seconds for some classes) when compiling (with SBT compile/JRebel reload or with Play compile/reload).

PS: Side note: Not to sound arrogant, but for the perception and spread of the language it is not important what Martin thinks, but in customer development style what my perception as the CTO of a company thinks that might decide between Scala and Clojure.