My best guess: I've found that with many woven fabrics, manufacturers will err on the side of caution and say dry clean or hand wash when they can actually be washed and dried, no problem; but if you ruin it in the wash, they're off the hook. Shrinkage could be an issue with silk (?) but if you swatched and washed the swatch as you would like to do with whatever you make, you'd know if shrinkage or something else is the issue.
Let us know what you learn or do, please, as ArtLady's idea of socks is appealing but I don't do hand wash socks.
I should never overestimate my basic arithmetic skills.