Actually, I misspoke, the amount of Pitch Bend that can be achieved in GB, is dependent directly on the instrument. i.e. many Drum kits sounds can bend up to 3 octaves, but Guitars will only allow bends of 2 semitones (which kind of makes sense, unless you wish to emulate a whammy bar). The book "How to Do Everything with GarageBand", on pg 168, also verifies this point as a special note: "Usually, pitch bend covers a range of two half-steps. But some instruments can be set to a pitch range of one octave or more."
However, there does not seem to be a means to change this range from within GB. Although, I did read a posting that if you bring a GB project into Logic, and edit it with exs24 you can change the range.
http://discussions.apple.com/thread.jspa?messageID=9310715
Ta again
Gary