Blender and other high-end packages can make anything from high-poly PS3 models to low-poly DS models.
It's not overkill. Pick your favourite package and make some cool low-poly graphics.
A similar comparison would be using Photoshop for pixel art, like you're doing right now. It's totally acceptable.
EDIT: In those videos you linked, the primary reason for the "old school" look is the use of low resolution textures, like 128², paired with Nearest-Neighbor filtering (Unity calls this filter mode as "Point"), which keeps your textures crisp and pixelated, further improving the look. This type of filtering you control in your material's textures or render-state settings in your game engine.
These small textures filtered like this and applied to low-polygon models guarantee you the old school look.
If you like low poly, check this great artist: http://tommytallian.blogspot.com.br/