Weird pricing like this happens sometimes.
The differences are as follows: the 6750 has a higher FSB (1333 vs 1066), lower multiplier (8x vs 10x), higher voltage (0.962 - 1.350 V vs 0.85 - 1.3525 V)
It's also almost a year newer.
Seems to be the replacement for the E6700, which would explain the odd pricing.