Why hasn’t Shopify enabled a Ship Rate based on Item Count option? If you can do it by weight and / or by cart value, it should be trivial for Shopify to add this option.
There are so many great things about Shopify that make the online efforts of a small shop owner easier. It seems totally out of character for them to force us to have to come up with complicated or expensive work arounds for this limitation. Especially when it would be so simple for Shopify to add this as an option.