Ultra, Sounds like you know your insurance. You are basically correct. If you have good medical insurance you do not have as much need for that part. Although even good policies require some payment on your part for care, have sublimits and/or exclusions for certain therapies, artificial limbs, convalescent care, nursing homes, long-term care, etc. If you were to become completely disabled, in addition to lost wages, rehab, etc., etc. you would very likely eventually lose your medical coverage after exhausting COBRA so you would have some financial risk there.
Even if you have disability coverage it usually only pays 60% of your past earnings and in most cases that is taxable. Over years that difference can add up.
Hopefully none of us will need it. You are correct it is expensive on bike policies. For most of us, if we get creamed by an uninsured driver or someone with minimum state coverage, it could make the difference between making it financially or not.
If you have great coverage elsewhere to cover those risks, you can elect to buy a lower limit (can't waive completely in VA) and save the $. In our practice we never reccomend that, would try very hard to talk someone out of it and then would require a signed waiver if a client wants to do that. It's not for the commission dollars I assure you. It is because we believe it is that important.