From what I can tell, the reason that games using smooth scrolling are rare on IBM PC is that while fine scrolling was documented on EGA, it wasn't possible on

From what I can tell, the reason that games using smooth scrolling are rare on IBM PC is that while fine scrolling was documented on EGA, it wasn't possible on CGA without undocumented demoscene style hacks. Amega and all the consoles had smooth scrolling in the base configuration, so many games used it. While EGA was introduced all the way back in 1984, most games were designed for CGA first, as there was a massive install base of CGA cards, with enhanced EGA/VGA versions. So really, the major innovation of the Keen 1-3 engine was actually the fact that it dropped support for CGA, allowing it to finally take advantage of EGA's smooth scrolling. Ironically, CGA was still popular enough that they released CGA versions of Keen 4-6 (1991). They simply scroll in 4 pixel (one byte) increments.