Why aren't my app icons showing up after installed?
Not all apps have explicit launchers (or app icon).
Take an example from Stereo Bluetooth Headset SBH52 app:

This application will not be visible in your phone's home screen. Access application settings via Smart Connect (LiveWare™ Manager), or via your phone's status bar.
(Emphasis added)

As for Exchange Server (or Exchange Services on Nexus stock ROM), it's only a back-end service used for communicating with Exchange server, with stock E-Mail app as its front-end UI.
Another example is Google PDF Viewer, where it's only prompted when opening a PDF file. (see How to open Google PDF Viewer app?).
If you want to force open the app, you might be interested in List all activities of an app.