For the record, I have no 3d printer nor 3d modeling skills nor interest. But on a random day I learned about layer height and width of home printing while completely having no idea what "20 nanometers" means for a game miniature.
Those resolutions and nomenclature only exist for 3D printers, which is why it isn't really comparable. And there are different technologies for 3D printers too to confuse things further. 3D printers use a material and then use a depositing system (some use just glue and air, others lasers, UV light, etc) to build layers a certain thickness, then build up layer by layer. This may also require the use of bracing (to be cut off later) to hold it while printing. It takes several hours for a single figure at a medium resolution (all differ). All 3D printed objects then have to be treated afterwards, depending on material I have heard of acid baths, sanding, isopropyl alcohol.
No matter what, 3D printed figures will be more delicate / prone to break than metal or injection moulded plastic of the same item.
In pewter casting (IWM), a mould is made out of steel from a master miniature (prototyped in 3D, sculpted, and finalized), and is then the mould is spun while melted pewter is added. This gets it into every crevase. Where the two sides of the mould meet you can get flashing (the little lines). If the sides aren't exactly aligned, this can cause the offset flashing you sometimes see on metal minis. The tags are locations where the pewter was fed in. This is considered gravity fed.
For plastics a sprue is designed and a large mould is created, typically this is around 4-12 different miniatures, though it can vary. Plastic is heated to very specific temperatures and injected under pressure into the mould via the sprues. The heat, pressure, and polymer used all go into the amount of detail it can hold, how flexible it is (or brittle), and so on. Again though, it all comes down to the sculpt detail. good sculpt = good detail (as long as you use the right plastic). the better quality and larger, the most expensive the materials.