I've searched on the web but still can't get a straight answer. Closest I came was Broadcloth is a plain weave but Homespun is a twill. Here in Australia what we call Homespun is a plain colour. What you call Muslin we call Calico. The LQS also sell what they call Quilters Muslin but which is actually Calico that has been processed more. The difference is the price. Calico $1.99 - $5.99 per metre depending on width and quality, Quilters Muslin $25.00 per metre. I buy Calico by the roll and process it myself. It ends up ivory/off white colour and is soft and lasts for years.
As for our homespun I think that must be what you call broadcloth but we now get different qualities (generally from India or Pakistan) but it's still only $7.99 per metre. I started using Moda Bella Solids a couple of years ago and like the quality very much. I know my BFF likes our Homespun. We can also buy a mottled one as well. Makes the colour a lot more subtle. I remember Broadcloth and Headcloth from school. Headcloth was used for handtowels and tray cloths.