but it is clear here that $blah in the "object" retains this as does $testob??

You are in fact modifying the package variable $blah, and like all package variables, are visible throughout the execution of the program. Whereas a new instance of $testob is being created every time as indicated by the value of $self->{blah} always being at 1 post-increment. See. perlobj for more info on objects in perl.