Take longer means less bugs which means less fixes which means happier people.
When it comes to software and especially operating systems, I would rather the developers take the extra time.
I have noticed (as a developer myself) the people screaming for the updates to come out early are also the first in line to complain when the early release doesn't work 100%.
Remember, while the iPad is BASED off the iPhone's OS, it is a different animal that has a lot of rewritten code to cover the new hardware in the iPad.
Relax, the update will come. Besides, how many of the "I want it now" crowd will be screaming for the JB the day after iOS4 for iPad is released...