The normal Metasploit installer installs its own Postgres and runs it on port 7337. The Kali Metasploit package uses the system Postgres which runs on standard port 5432. Nexpose installs its own Postgres, but attempts to use the standard port.

To fix this either:
a) Kali should run their system Postgres on a non-standard port
b) Nexpose should run their custom Postgres on a non-standard port
c) Nexpose should use the system Postgres on the standard port when available

My vote would be (b). I'll try to file a bug on Nexpose.

I agree with Brandon that if Nexpose needs it own postgresql instance then it should run it on a non-standard port. Hence this is not a bug in the Kali side.