A person has “control” (ba’alus) over his property, he can make his property hefker or gift it or destroy it, so because he has control over his finances, therefore he can place upon himself financial obligations (except for the financial obligation of a “knas” [fines] which is only in authority of Bais Din to impose). His hodaah can therefore be michayiv him financial obligations.
you should read the Ketzos I posted earlier (the above seems like the shitah of the Mahri BL) here is the link:
http://beta.hebrewbooks.org/tursa.aspx?a=cm_x8809
” won’t compare it to viduy, when a person confesses his sins, but shouldn’t his confession to Bais Din (a viduy of sorts) be accepted as part of his teshuva – that he is accepting responsibility for his past wrongs?!”
Actually, I once saw a Pshat why you say Vidduy before you go to sleep or before YK, that it works as ‘Hodah b’fnai Bes Din’ which is Pater from K’nas when testified before the Edus testifies, which is occurs later at night, through the act of Yad kal Adom Chosem Bo!