I heard same channel can be used to solve little bugs, if i'm not wrong.
Once i did click update, it looks like download more then definitions.
VPS Update can do more than just update virus definitions as you can see from my attached image, it does an 'Engines and Virus Definitions.' So it can update the scanning engines, without having to do a 'full program update.'
The only problem is it doesn't say that in the UI, it just says Virus Definitions.
Depending on your settings it only checks for VPS every 4 hours (default), but if you do a manual update check, and a VPS update is available you would get it then, not on the next scheduled 4hr check.