Tobiano does like white legs. It will try **** hard to get white on them. However, frame likes them dark just as much. Generally there is at least sabino or splash also present, which both like leg white, and so we have more white even if there is still frame dark on them. I suspect in this case that the mini only has frame and tobiano, so it is an "equal battle" if you will.
As for white socks - usually tobiano will have some white on the legs. More often than not, if tobiano is really minimal, it will be on the hind feet - provided nothing else is trying to stop the white being there. I have not ever seen a tested horse that has tobiano without leg white - but that doesn't mean it isn't there. The most minimal tends to be at least a white heel or something on a hind foot. This mare is tested homozygous for Tobiano, and is one of the most minimal I have ever seen.