This is actually not why it was done (I was there :P), and didn't really factor very much into the calculation at all. So your perspective, while interesting, was not the one used.
In fact, the business folks mostly thought it would be a downside (given all the FUD/etc around the time period).
Your perspective is also interesting because Apple did not go this route and still were wildly successful. So i disagree it "had to be open source or it would not have taken off". I'd like to believe that (really!), but there is an existence proof that this was not true (Apple), and in the end, i just can't bring myself to think what you say is true.
It was open because Andy thought it was best for the world (really. I realize how cliche that sounds, but if you've ever met the guy, you'd realize it was true. He gave pretty much not a shit about the business side of it, it's not what he enjoyed).
As mentioned, the business folks argued that this model would just lead to a shitty experience (among other things) over time. (This was pre-iphone, so apple was not a consideration at the time).
The compromise was "great, let's figure out how we can make sure that doesn't happen through branding guidelines/etc".
Later, after Apple was successful, the business folks all said "look, this model was a mistake, look at Apple". You could still push back and say "we are doing fine".
I don't see how, in the future, the business folks don't win every argument here.
Apple's model is giving them all the money, with none of the downsides.
This seems like a "business school case study" they would teach in the future.
