Well I am new to this site and here is my bit my of personal experience regarding BMW's, not as an owner, but a very close up observer.
In January I went along with several others, with Nick Sanders Lisbon - Timbuktu - Lisbon, about 8500 miles round trip. The most common brand was BMW, along with a 650 Pegaso, a couple of KTM 950's, a Honda Transalp and three XT660's, a Varadero and myself on a 955i Tiger.

This is what happened (DNF = did not finish)

Pegaso 650 - no problems
Transalp - chewed a chain, shot rear shock
XT660 - chewed 2 chains, bits fell off, bent swing arm? DNF
XT660 - shot shock
XT660 - Nicks bike, sort of generally got shook to bits DNF, may have finished but Nick ended up driving back up truck
Varadero - dinged wheel rim
Tiger - dinged wheel rim, rear brake lever lost argument with rock
KTM'S - no problems

but what of the BMW's?:

GS1100 - DNF, a big off, would have wrecked any bike
GS1150 - DNF, broken engine mount
GS1200 - fuel pump failed (almost new bike), luckily in Spain, got fixed
GS1200 - DNF, brake and suspension failure both at the same time
GS1200 - God did the clutch stink but finished
GS1150 - OE luggage fell off a few times, otherwise ok
GS1200 - no problems
GS80? - ancient but no problems

Obviously all the bikes ran on the same roads, tarmac, poor tarmac, apalling tarmac, rough track, rough track with lovely hidden soft sand, and those lovely corrugations of course.
This was my first venture into Africa but won't be the last, for sure it will never be on a BMW after seeing what happened to this particular bunch. Nope, I'll stick with my Tiger, which incidentally was carrying my 12 yo son as pillion and our luggage.
The bigger bikes made heavier weather of it off road, everyone had offs whatever they were riding but the BMW's did have problems that no one else suffered from, not rideability but reliability issues.
Thats my bit, make of it what you will.