I-94 clearly states day/mo/yr to prevent confusion for international visitors (who are used to this date format) and Americans who will be checking this form to verify eligibility for various benefits (SSA, DMV, HR, etc).

The UK visa does not mention the date format, it is just written in dd-mm-yyyy. I guess the reason is that the UK visa is intended for the UK where all people are accustomed to this format. The UK visa is not intended to be used in the USA.