They can, and I imagine will, make it available on web. But the iPhone Maps application isn't developed by Google, so they can't add it. It looks like Apple moving away from using Google maps, anyhow.

While the technology for making indoor map content (georeferencing a floor plan) is already widely available, most smartphones do a very poor job of positioning themselves indoors. GPS doesn't work inside, leaving cell and wifi trilateration as the most readily available alternatives.

Another likely factor for Google deploying on Android only is the ability to use wifi signal strength data from the phone to do approximate indoor positioning (the you-are-here "little blue dot"). Apple chose to lock developers out of the API for reading wifi signal strength, which limits the iPhone's ability to do indoor positioning (or show you nearby wifi routers).

In Apple's defense, the indoor positioning experience on Android does not meet the high expectations that GPS has set for users. Instead of a precise little blue dot, you get a 10-30m wide big blue circle. Some of the positioning hardware announced from chipset makers like CSR and Broadcom may improve this situation in the next generation of handsets.