According to Miyamoto. They were actually planning on making him collect fruit once:
http://www.officialnintendomagazine.co.uk/article.php?id=22376
"When we were thinking about something that anybody would look at and go 'I definitely want that!', we thought, 'Yep, it's gotta be money.'"
http://www.officialnintendomagazine.co.uk/article.php?id=22376
"When we were thinking about something that anybody would look at and go 'I definitely want that!', we thought, 'Yep, it's gotta be money.'"