I don't trust fabric to shrink equally in all directions, so that's part of why I pre-wash fabric. Plus there's a smell to fabric when I first bring it home - it must be the chemicals others have mentioned (though thankfully I don't seem to be sensitive to any of them).
Batting...I like the crinkle and so far I haven't noticed batting shrinking more in one direction than another, so I don't bother to pre-shrink. If it's something I don't want to crinkle I use poly batting. But usually I sort of depend on the crinkle to help distract from quilting boo-boos! ;-)