Proprietary doesn't factor into it. Maybe a clearer way to put the thing I am positing: the idea behind open source is that it is interesting end user apps that have value and change the world, not the software components from which those apps are built.
Right, it's the application/library distinction again. Developers might care a great deal, even if there's nothing interesting using it yet.
> open source was an explicit recognition that we care about and attach value to the big ideas that change the world, and that by making the building blocks freely available we caused more of those big ideas to come to fruition.
I suppose so, although the 'free' (as in price) component there can be separated out from Open Source. Freeware (software which is made available free of charge but which is not Free Software or Open Source) can also serve as a platform, but in practice often loses out to Free and Open Source alternatives. SkyOS is dead and gone, the Linux kernel continues to conquer the world.
The Open Source position is that Open Source is the most effective way to develop software, and of course it's had tremendous success in 'infrastructure' software (libraries, frameworks, operating systems, programming languages).
(This is quite different from the Free Software position, which holds that non-Free software is a problem in terms of power and control over users, quite aside from the question of how to most effectively develop software.)
We should be careful not to go so far as to say that Open Source is about enabling interesting/profitable non-Open Source programs. Copyleft licences are explicitly hostile to this, but are recognised as Open Source licences.