Resolution and quality, I hope. Most of these textures are 1024px or larger, and they're seamless/tileable, which makes them useful for repeating backgrounds or

Resolution and quality, I hope. Most of these textures are 1024px or larger, and they're seamless/tileable, which makes them useful for repeating backgrounds or 3D modeling. Also, the royalty-free license. A lot of DeviantArt users require you to link to them, or don't allow commercial usage of their art.