This is to preserve precious vertical space.  It is a much bigger deal when braces are not cuddled and the signal to noise ratio is 1:1.

Also this only really bites when there is no else clause and the 1+n lines are executed irrespective of the condition.  If there is an else clause, it is a normally a compile time error and this is caught very early.

I am happy to change this to "Braces may be omitted..."  That reflects more how I feel anyway :)