false:EXPRESSION vs not:EXPRESSION

is there any reason why petal uses false:EXPRESSION instead of  
not:EXPRESSION ( which is the way TAL is originally implemented) ?

it's easy to work around this, either with using 'false' in the  
templates or extending petal with a modifier to recognize 'not'

i understand the need for a perlish true/false vs the pythonic not --  
i'm just wondering why petal doesn't support it with an alias so that  
templates originally written for python or another implementation  
will work right out of the box.