Apache disallows the Facebook BSD+patent license

Well the current patent implied licences are judicial constructs meaning they're not supported by an explicit statute but instead come about in court by consideration of nearby laws plus common law expectations, yes. However, almost all of the constructs require some sort of promise about patents. It is thought (but not tested in court) that the patent non retaliation clause present in most open source licences constitutes such a promise. The problem for BSD is it doesn't have one.

The implied licence doctrine that doesn't require a promise is legal estoppel, which is currently constructed in terms of a sale of a patented item. The two requirements to invoke it are consideration and no non-infringing use (the estoppel theory is if I sell you an item which you cannot use in any way except by infringing a patent I hold, I can't then sue you for infringing that patent because my sale to you of the item is only effective if you can use it, thus the consideration I received from the sale must have implied a licence to my patent). No non infringing use is commonly considered to be satisfied if you make a contribution to an open source project which cannot be used unless one of the patents you hold is infringed, which works for BSD, but consideration is much harder to come by. Fenwick and West did an analysis of GPL in 2006 which suggested you could get to consideration in terms of the promise by the downstream recipients to distribute modifications under the same terms (GPLv2 clause 2), so it is possible legal estoppel works for some open source licences.

The problem is BSD imposes very few constraints on downstream recipients, so really has nothing in it that can be construed as consideration; thus Legal Estoppel doesn't apply in its current form. BSD, therefore, requires the creation of a new judicial construct of implied licence, which isn't impossible, but which would be risky to rely on because courts are wary of creating new judicial constructs.