One of the significant changes in the updated editor windows in R2012b was a change in the shortcut keys in Simulink for zooming. In R2012b and later, zooming is controlled using the scroll-wheel on the mouse (or Ctrl+Scroll depending on your preferences). The keyboard shortcut keys for zooming were assigned to the much more standard zoom shortcut keys of Ctrl++ and Ctrl+-. However, these keyboard shortcuts more difficult to use with one hand on the keyboard and one hand on the mouse (a common practice for long-time Simulink users).
This function enables the use of the pre-R2012b keyboard shortcuts in R2012b and later:
r: zoom in
v: zoom out
1: Normal View (100%)
f: fit selected block(s) to window

This simply adds these shortcuts, and does not deactivate the use of Ctrl++, Ctrl+-, or the scroll wheel.

To apply the customization, from the .zip file extract the file sl_customization.m and put it somewhere on your MATLAB path. At the MATLAB command prompt, run sl_refresh_customizations. These customizations should then appear in the Simulink->View menu and the keyboard shortcuts should be active.

Note: for some reason the first few attempts to use this after registering the customization are very slow. However, it seems to then behave normally after that. I have not yet figured out why.