"How's a compiler faster than an intrepreter?"
Err. Because it generates native code? Or are you talking about the actual done-once compilation? All RISC OS development I've done for years and years has been on a Linux box. Compilation is essentially instant.
"How's fumbling around with bits in C more reliable than BASIC snippets?"
Only amateurs or the disinterested fumble. Everybody else crafts something beautiful and elegant.
"How's lenghty C functions more readable than BASIC?"
Casting, structs, type names in function prototypes, block comments, finer-grained variable scoping all make code much much much easier to read.
"How do you square readability as being opposite to code density?"
"C's best for serious programming."
Which NetSurf is.