I don't know if that's the reason, but there's no reason formatted output HAS to:

1) block at the caller, ever

2) have its data parameters pushed onto the stack

3) print all or nothing to a single buffer

4) identify the data type or modifier by the first letter of its English name (int, long, etc)

5) have its core modified to add functionality

Unlikely, unless the output stream's buffer is full, in which case you pretty much have no choice but to block. stdout/stderr are two channels one generally should not write to in a nonblocking fashion.