Thanks Batman ... took a while to register and even longer to get to the relevant part of the GEN section, but finally got there. I've read it most thoroughly and can't see any reference to the speed limit being related to terrain clearance. Unless I've missed something, I suspect that you've misconstrued the situation because of the reference in the heading :
"Part III Procedure Construction and Obstacle Clearance Criteria for Instrument Approach Procedures"
This is merely a repetition of the heading used in Doc 8168. It is used there for convenience because Pans Ops is all about obstacle clearance. Whether or not significant obstacles exist in the vicinity of any particular airport or not.
I suspect that the UK CAA's differences need to be read in conjunction with their other publications. That might suggest, as reynoldsno1 said, that the reason is probably more related to tight airspace constraints than to terrain clearance.
Anyway, thanks for the reference. Seems like I could have applied a similar speed restriction here ... sure would be helpful in reducing the size of procedure protection areas!