And really, I think it's a matter of style.
It's no different, calling 'Chapter 1' a Prologue rather than 'Prologue' Chapter 1. You have to lay the same ground, have to introduce the same characters and setting.
Agents are against prologues, and I can't figure out why.
Take 'Harry Potter and the Sorcerer's Stone', for instance. We are treated to a 17-page first chapter, half of it detailing the daily life of the Dursleys and half of it a conversation between Albus Dumbledore and Minerva McGonagall.
My prologue, which is on its way to being written right now, (edit: Just got it done. I'm rather proud of myself! Onto chapter 2), is going to function in a similar fashion.
Blagh. I just hope my potential agent likes it, regardless.
If they want to call it a Prologue, they can. If they want to call it Chapter 1, that's fine too.