Bad example. 1/0 produces a compile-time exception in 5.8. Once you fix that, both behave identically and contrary to the OP's results. 
use warnings;

my $denum = 0;
eval { local $SIG{'__DIE__'} = sub { die $@ };
     print 1 / $denum;
};

print "[$@]\n";

[download]
>c:\progs\perl588\bin\perl script.pl
[Died at script.pl line 4.
]

>c:\progs\perl5100\bin\perl script.pl
[Died at script.pl line 4.
]

[download]
This is perl, v5.8.8 built for MSWin32-x86-multi-thread
Binary build 817 [257965] provided by ActiveState http://www.ActiveSta
+te.com

This is perl, v5.10.0 built for MSWin32-x86-multi-thread
Binary build 1001 [283495] provided by ActiveState http://www.ActiveSt
+ate.com

[download]

In reply to Re^2: 5.10 shows uninitialized $@ warning by ikegami
in thread 5.10 shows uninitialized $@ warning by pmSwim

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