Windows 8.1 is more substantial than a traditional update and Microsoft wanted to make it very easy for customers to consume as well which is why it will be delivered through the Windows Store. It's important to note that when describing the update, she did not say that it was a service pack, but an update, which ties into the belief that Microsoft is done with the traditional service packs and will move to more prominent releases like Windows 8.1.
Reller stopped short of saying that we will see Windows 8.2 and beyond but wanted to hit home that Windows 8.1 is a large update for the platform and that it will bring many enhancements to the end user. We would have loved to have heard that we would see Windows 8.2 next year but we will be content to know that Windows 8.1 will be free and a public preview will be released on June 26th.
Not long after the release of Windows 8 we started hearing rumors about the rapid release cadence that Microsoft was moving towards with many of its major platforms including Windows. Seeing that Windows 8.1 is the first step in the process, we will be quite curious how long it takes Microsoft to move to the next phase of the Windows 8 release cycle.
Source: JP Morgan Technology, Media and Telecom Conference