You might notice that the gear does have a Mach as well as a CAS limit, for the very good reason that gear may be used in an emergency descent from high altitude in the event of speedbrake failure
Most interesting observation re use of landing gear for emergency descent. Any chance of quoting the published reference? I would have thought the probability of having a emergency descent event and by rotten luck or a quirk of fate also having an inoperative speed brake at the same instant, would be a million to one...
On the other hand as there is no altitude restriction on landing gear use, it makes sense to have a mach number restiction as well as IAS limit