Yes, I guess the mouse wheel action has become a default setting in QGIS 2.16.x. If you go to
Settings > Options > Map Tools > Zoom factor, you will see the minimum value possible is
1.1. Makes sense since a factor of
1 for a given value will remain the same. So let's change the zoom factor to
1 using Python!
Paste the following in the Python Console:
from PyQt4.QtCore import QSettings
For QGIS 3.x:
from PyQt5.QtCore import QSettings
Restart QGIS and now your mouse wheel has become 'disabled'.
Note that the zoom factor will always be shown as
1.1 as that is the minimum value allowed to be shown in the widget. Also, if you go back to the Options menu and you click OK, the zoom factor will be reset to
1.1. So you will need to use the code and restart QGIS again.