I chuckled that Twain humorously was complaining about nouns coming after wegen being in the genitive case. After all, it parallels with the 'of' in English analogue, 'on account of'; 'of' in English is used to mark notions that most Indo-European languages that still retain a genitive would express in the genitive. One still frequently encounters the vestige of the English genitive case: it is the -'s or the -s' that one affixes to words to indicate that the word signifies the possessor of some other word.