Each individual printer will have its own default margins. IF your printer will print any closer, it will be somewhere in the driver software - so it *should* be an option within your print window. FWIW - I have also found that sometimes the Mac drivers are less robust than the PC drivers. (Frustrating, I know....)
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MacBook Pro 2.0GHz quad-core Intel i7
IMac 27" 3.4GHz quad-core Intel i7