Male pattern baldness is a caused by a single gene, is a recessive sex-linked trait, and is only carried on the X gene (females are XX, males are XY). If a guy has male pattern baldness, he's XbY (I'm using the lowercase b to indicate the "baldness" gene). A woman can have "male" pattern baldness, too, but has to be XbXb. A woman who is XbX is a carrier for the trait, but won't express the baldness trait...she could have really thick hair. Since men get their X gene from their mom (and their Y gene from their dad), if they go bald, it means their mom was a carrier for the trait.
So, Sherry, I can see why your husband started balding early, because it sounds like his mom very well could be XbXb (due to having thin hair), or even if she was XbX, your husband could have gotten that "bad" X gene from his mom, making him XbY. Your mom could be a carrier (XbX), and passed her "good" X onto your brothers (who would be XY) and her "bad" X onto you (so you'd also be XbX), and then you passed that "bad" X onto your son!
Sorry, sometimes my dorkness comes out (I have a PhD in plant breeding and genetics, so love figuring stuff like this out!)
As for why they can figure out male pattern baldness and not IBD, it's relatively easy to figure out inheritance of traits that are caused by a single gene with two alleles. Once you know the different patterns to look for, it's pretty easy to determine if it's sex-linked, recessive, dominant, etc. ;) Since it's pretty apparent that there are a number of genes involved with IBD, it just muddies the picture that much more.