Zend Raises Another $9 million - For What?

From the 'Funding Mature Companies' files:

Zend, one of the lead commercial PHP vendors, today announced that they have received another $9 million in venture capital funding, led by Greylock Partners.

While that certainly sounds like good news on the surface - an open source vendor getting money etc - Zend isn't exactly a startup still is it? Zend has been a successful (as far as I can tell) vendor for over 6 years.

According to Zend, they had record sales in 2009, adding 4,000 news customers. They now claim to have more than 1 million registered users for its PHP solutions which include the Zend Studio IDE and Zend Server PHP efforts.

So my question is - if Zend is already successful, both in terms of technology and customers why does it still need additional venture funding? At this point, shouldn't revenue and cash flow from operations be enough to keep the company going?