Not true.

use Data::Dumper;
[download]

is the same as

BEGIN {
   require Data::Dumper;
   Data::Dumper::->import();
}
[download]

Like psini already said, the problem is that Perl already had to decide whether Dumper is a function call or not before use Dumper; was encountered.

1. Compile my %test_hash = ( a => { b=> 'c' } );
2. Compile print Dumper %test_hash; (Dumper is treated as a *Dumper since no function named Dumper was found)
3. Compile use Data::Dumper;
4. Execute require Data::Dumper;
5. Execute Data::Dumper::->import();
6. [ Script has been compiled. Now start executing it ]
7. Execute my %test_hash = ( a => { b=> 'c' } );
8. Execute print(*Dumper %test_hash);

You can only omit parens on a function call to a function that's already been declared (but not necessarily defined) or if you annotate the function call with &.

Update: Added list showing execution flow.