It's likely that the iPhone software engineers have been working heavily on bringing up the iPad, as well as creating the iPhone OS 3.2 SDK, and thus not able to work on adding new functionality to other devices running iPhone OS 3 (i.e., iPhones and iPod touches).
There is evidence that Apple really doesn't have the necessary resources to keep up with their intended software & hardware release schedules, thus things slip. Steve himself has admitted to it once or twice.
For a company of its size (in terms of revenue, etc.), Apple is actually lightly staffed. They would really execute more comfortably if they hired some more engineers. They have enough cash, they can afford to hire a few more folks.
Even with hiring new people will take months to get them comfortable with the software and sometime it can slow down the development process overall. Not every programmers can start coding immediately. I do believe Apple has already posted several job postings for iPad/iPhone divisions as indicated by a few news posting about it over the last few weeks.
I am not sure why Apple hasn't expanded their resources, it sound like Apple prefers a small team of excellent engineers instead of a large team of good engineers. Not to mention that I don't think Apple has a lot of experience in dealing with multiple different divisions at same time, it is very hard to manage a company with diverse products. Even larger companies like MS have a history of management issues.