Bluetooth vulnerabilities

Reading about the possible attacks that can be performed against
Bluetooth devices, I have 2 questions.

1. Why some Bluetooth phones are more vulnerables than others, not
considering the PIN length? Is is because Bluetooth is weakly
implemented in those phones?

2. If a Windows computer is equiped with Bluetooth and considering all
the possibles attacks that can be done, what is the worst damage that
can actually be done? Gaining access to Outlook's address book? I'm
not talking about hypothetical damages, only about what can currently
be performed by attackers.

Thanks.

Paul S