Sorry for the delay.
I just turned the N4 on, let it wake up and finish downloading some app updates. Then I plugged it in to this Win7 laptop and looked in Winders Explorer. The Nexus 4 shows up as a drive:
Nexus 4
- Internal Storage
-- .mmsyscache
-- Alarms
-- Android
-- chimani
-- DCIM
-- Download
etc.
etc.
I copied a bunch of photos from it (-Internal Storage -- DCIM -- Camera) to the laptop via the Winders GUI just fine.
In short, it seems the USB access to the internal storage (still) works fine.
Android Version 4.3
Build number - JWR66V
HTH.
Cheers,
Scott.