this is really true. Some insurances will NOT cover it on a home owner's policy if it is a large amount. You need a special rider for it.
Some won't do it if you have a STUDIO because then you are business in their eyes and they don't insure business with a home owner's policy.
Truly if you have a large stash, machine collection, etc, you really need your insurance company rep. to come in and walk it/talk it out to make sure you are covered correctly!
We had to get a rider for my DH's wood shop, one for my quilting studio and one for my jewelry!