You seem to be describing the "surface area" of the impact after an exploit has occurred. I was trying to describe the attack surface area the would allow an exploit in the first place. This is limited to a single site for the manager scenario - the main password site. In the reuse scenario, you are impacted if any one site has an exploit against it (Twitter, Facebook, Slashdot, site XYZ, etc...) - thus much larger attack surface area.
The number of your accounts exposed after a successful attack is the same (assuming you reuse the password on all sites that would otherwise be kept in the management site). You're correct that the management site would give your attacker a nice convenient list of sites to target. I'm guessing without that the attacker would have a end-target in mind anyway. Perhaps they'd check all the mail services (GMail, Outlook, etc). Then move on to social media (Facebook, Twitter, etc). They might even check financial sites (Paypal, banks, etc).