That's what I've always thought, too. But I'm sure DC wants to make it so that Metropolis and Gotham have show no similarity to any ONE city. That way, they seem more unique and real in the DC Universe.

First, you need to know (if you don't already) that "Gotham" was coined as a nickname for New York City by writer Washington Irving in 1807. The first time that Gotham City is actually named seems to be in
Batman
#4 (Winter 1940). Comics artist and historian Jim Sterenko got the origin of Gotham City from
Batman
writer Bill Finger:
Writer Bill Finger is credited with the creation of Gotham City. Finger commented on the naming of the city and reasoning for changing Batman's locale from Manhattan to a fictional city: "Originally I was going to call Gotham City 'Civic City'. Then I tried Capital City, then Coast City. Then I flipped through the phone book and spotted the name 'Gotham Jewelers' and said, 'That's it', Gotham City. We didn't call it New York because we wanted anybody in any city to identify with it."[1]

1. Steranko, Jim (1970). The Steranko History of Comics. Reading, Pa.: Supergraphics. pp. 44. ISBN 0-517-50188-0.
   Link:
   http://en.wikipedia.org/wiki/Gotham_City
   "If I'm going to have a
   past
   , I prefer it to be
   multiple choice
   !" - The Joker

You are correct, dave. And, when Metropolis was first mentioned by name, its location was given as the state of New York.
"If I'm going to have a
past
, I prefer it to be
multiple choice
!" - The Joker

In the earliest Superman adventures, Superman was in the actual city of Cleveland, it wasn't until later did Metropolis become it's own city.

Jerry Siegel was born and raised in Cleveland, Ohio. Joe Shuster was born in Toronto, Canada; he moved to Cleveland with his family when he was nine years old. I have no idea where you are getting Vancouver from. It would probaby be more accurate to say that Metropolis was based mostly on New York City, with elements of Cleveland and (maybe) Toronto added in.
"I'm willing to put my life on the line to do what I have to. But it has to be mine, no one else's." -
Batman: Gotham Knight

Your basting this assumption only on the current Superman and Batman movies. Gotham City was based on New York when the Batman comics was written. Metropolis was based on the creators hometown in Vancouver, Canada and several other major cities in the US including Chicago.

Gotham City was indeed originally based on New York City, where the infant comics industry was located. "Gotham" is even a nickname for NYC. Batman's earliest golden-age adventures were based in New York. His base-of-operations gradually evolved into the fictional Gotham City. You can easily identify Batman's base-of-operations as NYC as late as
Batman
issue #3 (Fall 1940).
That's not to say that Chicago didn't inspire some of the corruption and mobsters of Gotham City.
"I'm willing to put my life on the line to do what I have to. But it has to be mine, no one else's." -
Batman: Gotham Knight