The problem is that Android phones range from 2.5" displays to 5" displays, so you can't make a "one size fits all" dock or even anything close to it. Plus a lot of popular Android phones are way bigger than single-DIN, whereas the iPhone is just a bit bigger and can be shoehorned in (as the product you link). And, even though most Android phones are microUSB, not all are, especially globally, and the USB port is in a totally different place on every single one. Plus you'd either have to plug into the headphone jack (another connector that's in different places on every Android phone, and not even present on some) or write an Android application that did audio over USB (hard and would require a bit more hardware and software on the radio side).

The iPhone makes things easy: all of the models are nearly the same size, there are only a few basic shapes (2 or 3, depending on if you count the now-outdated original iPhone) and the dock connector has both communication and audio and is in the same place on every phone. If you construct the dock connector so that it can latch onto devices of varying thickness, you can even support the iPod touch family with the same basic design.

Also, the iPhone understands the old serial iPod dock protocol, which lets you perform simple music playback tasks like volume control and track navigation without writing a custom iPhone app or licensing the (expensive) Apple Dock API.