In your best Top Gear voice:
"Some say that SANs are immune from file fragmentation - and that it just doesn't matter. Others say that they automatically cater for it - and that's why they are expensive"
All we know is that they're wrong !!!
If Windows is spending time handling and issuing split I/Os chasing different parts of a file, it's not performing optimally. These requests take time and it adds up.
We have evidence proving the benefits of defragmentation but If you think we're wrong and can explain why, with a before/after comparison showing no improvement on a SAN, we'd love to hear it.
Better still why not see for yourself and try Defrag.NSF, it's that easy!