This analysis makes a good point: By staging major attacks to coincide with US policy initiatives, Hamas is in effect saying that "The US doesn't call the shots - we're the ones call the shots".

This time around the US is attempting to impose reform the PA and shoehorn everyone into an awkward agreement (which the EU would likely consider an expression of vast arrogance if not for the fact that they have been urging something similar) - and the PA wasn't happy about it.

So it's total speculation, but: maybe Bush delayed the speech not just for propriety's sake, but because the administration started to think that maybe it had been reaching too far.