OK, this thread is eye-opening, lol.
Can someone explain (or link me to the post/site) how this change is accomplished? I mean, some games change generations!
Easy. The DS had a garbage resolution(192p, lower than the snes) and zero texture filtering capabilities. It did however have quite a bit of RAM (4MB, 16MB for dsi) and could store decently large textures even if they weren't filtered.
In short, the system was heavily held back by it's screen and final ability to output higher resolution. Emulators can get around this, allowing arbitrary resolutions and the effect is quite marked.
Holy nearest neighbour filtering Batman.
Identical to real hardware. Honestly, most times you wouldn't want to filter them because they won't line up correctly. Textures designed on systems without filtering tend to be more "random" to break up the edges and prevent you from easily seeing a pattern in things like floors and walls. If you filter these they often make things look like they are built of blocks (which they are, but again that defeats the purpose).