Do you have specific benchmarks to back up this claim? I think it's completely unfounded. Every test we've done against C and C++, we're competitive. Exception is the performance of the IO/task runtime, which still needs work, but is unrelated to the language.
There's also the factor of immaturity: the language is young and changing, so it hasn't really been possible/sane to spend the effort writing high-performance micro-optimised libraries for various tasks.
