The point is that the passwords on all of the accounts are different. Thus, the compromise of one service does not impact the accounts on any others.

That doesn't mean I don't care if my Dropbox account got breached because the password was in plaintext.

I suppose there are cases where someone got the dropbox password hashes and didn't own dropbox enough to have access to your dropbox account without reversing your hash. However, in most cases where plaintext passwords are exposed, the attacker will own your account at the service that was attacked because they are already inside that system.

If the DropBox passwords are leaked I am going to change my DropBox password whether it was hashed properly or not. The difference is that I won't have to change my password on dozens of other sites.

Plus 1Password has a sort of watchtower setting which shows you which websites had know security issues since your last password change, so you can stay relatively secure all over the place.