By my understanding, blah is a required integer value, but when i invoke my script without a blah arg, i still get a true result

What is "required" here is the integer value, not the parameter itself. That is, specifying blah without specifying a value will fail:

perl -w getopt_test.pl --blah
Option blah requires an argument
result = 
Use of uninitialized value in concatenation (.) or string at getopt_te
+st.pl line 9.
blah =
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Quoting from the documentation ...

GetOptions does not return a false result when an option is not supplied

That's why they're called 'options'.

... which says it all really ... :-)