Do you really think that a deed that says FS voids all existing leases? According to your line of thinking there is no such thing as a leased fee. I think the legal profession would disagree.
Of course the deed will say Fee Simple. Otherwise the buyer would never have any interest other than Leased Fee, or whatever other interest is indicated or conveyed by the deed. The buyer would never have the reversion of the property at the end of the lease(s) at which time he would normally get the FS. He would only have the LF estate and associated rights that were conveyed.
From what you suggest, anyone that receives a deed to a property that says Fee Simple doesn't have to be concerned about mineral rights that were previously leased to a drilling company? Or water rights? He gets FS, the deed says so, the leases don't matter anymore because the deed said Fee Simple.
All anyone needs to do is read the definition of leased fee/leasehold rights. Its really not that difficult to understand and it shouldn't be ambiguous to anyone in the real estate business. Why some appraisers are afraid to use correct terminology confounds me but apparently the facts aren't going get in the way of some ingrained confusion.
READ THE DEFINITIONS IN ANY APPRAISAL TEXTBOOK!!!!!
Have fun, I'm done here.