Ugly 3D printing with high precision
The 0.1mm refers to the thickness of each layer. However, it does not say anything regarding:


How precise the layers are in the XY plane
How precisely each layer is aligned with the previous in the XY plane
How consistent the extrusion is: are all the layers printed with a consistent line thickness


No matter how fine the layers (and these printers that you refer to can definitely print 0.1mm layers just fine); if they're not well-aligned with each other, or the filament extrudes inconsistently, you're going to see the layer lines. It takes a rigid printer, with low-play bearings, a well-calibrated extruder and filament with a consistent diameter to get smooth-looking prints (but you will always see some layering, especially if you look up close). Also, since filament is extruded in a round shape, the sides of the object are not perfectly flat, but consists of many small arcs, which makes it easier to see the layer lines.