Shutter actuation numbers don't mean much of anything, unfortunately. Some people think that it's a guarantee claim. It is not. It's marketing gibberish. The camera companies are very careful in their wording in an attempt to avoid an implicit guarantee, though I suppose a good lawyer could easily call them to task in a class action suit if it was found that the average shutter life was far lower than the number in those marketing materials.
It's also not a MTBF (Mean Time Before Failure) number. It appears to be a faux standard, as in "we took a bunch of these shutters and testing them X times and they didn't fail more than we expected." No one specifies how many parts were tested, how the tests were conducted, how many failures were allowed (though the wording implies none), or whether they tried going further than the number stated to see just where the MTBF value was.
In Nikon DSLRs, we now have some commonality: the consumer DSLRs all tend to be rated, um, excuse me, tested between 50,000 to 150,000 shutter actuations; the prosumer and pro DSLRs all list 150,000 actuations or higher. I suppose that is to suggest that pro camera shutters should last longer than consumer camera shutters, but I think we all knew that should be the case without the misleading numbers. Frankly, shutter failures can and do occur, but they seem to be one of the less frequent causes of a DSLR needing a repair (unless, of course, you were cleaning the sensor when the shutter closed on you unexpectedly).
And in case you weren’t paying attention, a large number of D600 shutters—which were rated to 100,000 actuations—began failing by throwing debris on the sensor within 5000 shots. So much for 100,000 actuations.