First, you have to get all of your hardware on the same OS.
If it were only that easy! That might make it easier for administrators, but it's not realistic in a work environment with different departments needing different apps, and older equipment using an older OS version (and working fine-- why risk breaking it?). Keeping it to 3 or 4 images is more realistic. It is still pretty with ARD to create groups broken into different images, though.
And using a scheduled script in ARD as mentioned above is still pretty easy to allow the clients to download their own updates.
