> * What was clear is that the success of their platform absolutely depended on applications not giving the platform a bad name.*
Yes, but I see this as Apple desiring tight control, first and foremost (as you hint at). Helping cut a potential malware problem off at the pass was a nice side benefit. I see the flow of causation in the other direction here. Apple just wanted control, because that's just how they do things. Initially they weren't even going to allow third-party apps.
This cuts both ways: while you can't distribute obvious malware on Apple's App Store, you also can't distribute perfectly benign things that people want, but Apple has decided is distasteful... to them.
> By contrast Google was deliberately creating an open platform on open sourced software.
I think that's a fairly naive view of it. They believed that open-sourcing the OS was the best way to gain market share (which worked, for all Android's fragmentation and faults). I sincerely doubt it had much to do with some desire for openness; that would contrast pretty sharply with most of the rest of Google.
> Their decision to lock down this piece was opposite the rest of the product direction.
Except they didn't lock it down! I have several apps on my phone installed via F-Droid. The Facebook Lite app used to (I uninstalled FB a couple years ago, so not sure if it's still the case) have the ability to manage and install its own updates (I assume for lower-spec/non-Google-Apps phones in developing markets). If I feel I can trust an app I download off the internet, I can install it. I have a couple of my own apps installed on the phone, without needing to pay Apple a $99 gate-keeping fee, and the software to install them is open source, not wrapped up in proprietary Xcode.
I will be the first to agree that most people don't avail themselves of this option, and an app developer who doesn't publish in the Google Play Store is kneecapping their market reach. But the fact that it's possible (and not even difficult) to do is the point. Sideloading on an iPhone is something that costs money; requires specialized skills, tools, and a particular brand of hardware; and is out of reach for the vast majority of people who (for example) would otherwise sideload on Android.
> * And it is hard to believe that they weren't looking at the demonstration of what happened with the iPhone and were trying to replicate the revenue model.*
I'm sure that was part of it, but... so what? I don't really see this as indicative of a particular mindset.