There is just one plist. It may be possible to specify a different value for the iPad for that key but I'm not sure if it's supported for that key.
It doesn't sound like a huge deal really. You could just remove it from the plist and set it programmaticly. It looks like if you try to set it on an iPad it just sets the status bar to black, so there's not too much reason to even check the UI idiom....
Anyway, see the Information Property List Key Reference docs if you want to try it.
In iOS 3.2 and later, applications can
designate keys in the Info.plist file
as being applicable only to specific
types of devices. To create a
device-specific key, you combine the
key name with some special qualifiers
using the following pattern:
key_root-~
In this pattern, the key_root portion
represents the original name of the
key. The and
portions are both optional endings
that you can use to apply keys to
specific platforms or devices.
Currently the only platform you can
specify is iphoneos.
To apply a key to a specific device,
you can use one of the following
values:
iphone - The key applies to iPhone
devices. ipod - The key applies to
iPod touch devices. ipad - The key
applies to iPad devices. When
searching for a key in your
application’s Info.plist file, the
system chooses the key that is most
specific to the current device. For
example, to indicate that you want
your application to launch in a
portrait orientation on iPhone and
iPod touch devices but in
landscape-right on iPad, you would
configure your Info.plist with the
following keys: