If you're using the CRT controller register to scroll, you can do smooth scrolling if you want. It's not a cunning stunt, it's just part of the interface you're using (or maybe it's not, there's a lot of references to various VGA devices not having the same behavior; I don't have lived experience trying to get these things to work, and most applications I used in VGA modes were likely to be conservative and use the part of the spec that worked).
If you're not using the controller registers to scroll, and you're just blasting scrolled text into the video memory... yeah, you can't get smooth scrolling with that. But you're also missing out on hardware accelerated scrolling, so :P
You don't need tricks to do it with VGA. There is a register specifically for that purpose. You can do it with CGA as well but that does require tricks.
(Like reprogramming the CRT controller on the fly to have reduced height lines at the top and bottom of the screen while doing the smooth scroll).
