Some texture packs have grass that varies greatly biome-to-biome, yet side grass is always the same. There are mods that change the texture packs so side grass is biome specific also, but they're outdated. It would be a fairly simple thing to add, and it would make grass look a lot better for people who don't use the default texture pack.
If you're a small map maker, send me a PM and if it's good enough I'll advertise it in my sig.