Hm... Well, yes, but since these machines have automatic water level control, the pre-wash should be able to thoroughly saturate a bulky item, by adding more water as the item soaks it up. To my thinking, the big problem with bulky items such as poly-filled comforters, is that they can tend to shed water, and take longer to get thoroughly wetted than smaller, less bulky items. A prewash (which also has occasional tumbles) will avoid this issue. I'm not sure that a bulky/autosoak setting would do much better.
My Neptune has a presoak option, which works well on bulky items.