One-day/One-park ticket -- Provides one admission to your choice of the Magic Kingdom Park, Epcot, the Disney-MGM Studios, or Disney's Animal Kingdom Theme Park. Valid for admission to one theme park only. $53.25 for adults (includes tax) and $42.60 for children ages 3 to 9 (includes tax) (1/03) This ticket does not allow park hopping.
2 Day/2 Park OR 3 Day/3 Park ticket - These are the tickets that were originally known as "bounce back" tickets when they first came out. You can only purchase the 2 day and 3 day passes at a WDW ticket window or Guest Relations. You can not purchase them over the phone, at a
Disney store, at any Disney off property ticket source, or online. These tickets allow entry to only ONE PARK per day. You cannot park hop with these tickets but you can leave and return to the same park the same day. Be sure to get a hand stamp before leaving.
2 Day/2 Park ticket - Adults $101.17 (includes tax) child, $79.88 (includes tax) expires 4 days from *purchase*. (1/03)
You save $5 off the price of two single day tickets.
3 Day/3 Park ticket - Adults $149.10 (includes tax) Child, $117.15 (includes tax) expires 6 days from *purchase*. (1/03)
You save $10 off the price of three single day tickets.
NOTE: Second and Third Day options MUST be bought *at the time of purchase of the first day* OR *before the end of the business day of the date of the first day's purchase* --- NO EXCEPTIONS. If you come back a second day and say you want to upgrade, you cannot. You will be buying a new One Day Ticket at Full Price. There are no discounts on these tickets other than stated above.
Guest's NAMES will now be added to One Day/One Park Ticket Media and ID's will be (randomly?) checked. NOTE: Guests will be limited to a purchase of SIX One Day/One Park Tickets at a time. (1/01)
(Bolding mine)
So, yeah, it looks like you get a small discount if you buy the tickets on the same day as the first. I think.