Any reason why the Rothchilds never show up in these lists? My best guess there is some sort of "who's the richest game" for some new money players (who's fortune can be tracked), where old money prefers obscurity.
Basically, after three generations a single persons wealth is distributed out enough to get dropped from these sorts of lists. Jeff might be the 2nd richest in the world - it's highly unlikely his grandchildren will be ranked as such.
A bank in London had no reason to cash a check drawn on a bank in Paris, or value a Letter of Credit given by a bank in Frankfurt, unless the London bank trusted the other bank would honor the liability, and honor it timely. This was especially true the larger and more complex the transaction.
As a banking consumer you wanted to use a bank that would honor instruments from and have its instruments honored by the most and the most important banks across Europe. Those banks were often part of a consortium of family-owned banks, because under economic stress the family-owned banks would always honor their commitments to each other, and offer each other low-interest loans to help another member bank stay afloat.