A blogger wrote:
«The couple could not find a rabbi who would allow a "change" in the ketubba, the marriage document, that would delete the word de-oraita, as Tosafot claims that the woman's 200 zuz claim upon the husband is Biblical. Since the ketubba is a court enacted institution, a tenai beit din, it seems that the Tosafot claim is hyperbolic, not essential, and based upon reasoning that is given to challenge.»
The institution of Ketubah is a d'oraitto requirement as per Ashkenazim
The d'oraitto Clause is not actually about the origin of the obligation
Rather it refers to the stricter and larger d'oraitto definition of zuz [viz. Zuzei d'Oraitto]
See SA Even Ho'ezer 66:2 Rema, and Levush quoting the Rosh that all state clearly that the issue is the smaller "Zuzei derabbanan" vs. The larger Zuzei d'Oraitto - and do not at all address the institution per se
It's sad that the poster and the attendees at the wedding did not appreciate the accepted philology of the adjective "d'oraitto" in Ashkenazic Ketubbot. A little learning might have gone a long way!