It's default because it's the easiest and fastest (except for "none" of course), not because it produces the best results, especially when it comes to the art.
"None (nearest-neighbor): Use when you want absolutely no sampling (blurring) of the image. Not bad to have.
Linear: Use when you have very small text; cubic interpolation is usually better otherwise. This produces blurred, but jagged, edges.
Cubic: Use for most images. Unless the image is very small or incredibly detailed, cubic and bicubic interpolation helps keep edges smooth. According to Wikipedia, it can sometimes increase perceived contrast or cause artifacts.
Lanczos: This interpolation method is much like cubic except that instead of blurring, it creates a "ringing" pattern. The benefit is that it can handle detailed graphics without blurring like the cubic filters."
So, as you can see, any serious enlargement requires the most sophisticated algorithm to prevent blurring.
