To answer your last question: have a look at webpd:
https://github.com/sebpiq/WebPd

There's a simple demo patch here:
http://sebpiq.github.io/WebPd/sound-check/sound-check.html

That's Pd's basic audio engine and message passing system running in javascript.  So in terms of open source, the efficiency is undeniable.  To run Max/MSP in a web page, they'd have to figure out some complex way to protect their proprietary code while still making it possible to make sounds by adding a script in the html.  The only practical thing I could think of is running a centralized service, but again that costs money and maintenance where a decentralized lib like webpd runs on the user's device.

Addressing the oddity of using proprietary software (IOS) to point out the benefits of open source:

Unfortunately the open source definition was designed to subtly hide the ethical reasons for doing open source development.  The reasoning for this was quite straightforward-- "share with your neighbor" doesn't attract business dollars.  So open source advocates focus on efficiency, like the ability to plug a 3-clause BSD-licensed library into just about any device you want, even a device that is locked down and requires the final app to be proprietary.

This is equivalent to teaching the scientific method, but downplaying the importance of reproducibility for some seemingly practical purpose.  If enough scientists are weak on such a fundamental aspect of their job due to bad education it will degrade their ability to carry out meaningful, reproducible experiments.

So open source advocates can't have it both ways.  If they purposely exclude the golden rule and "user freedom" from their marketing materials because it's such a drag, I don't see how they can complain when the efficiency of their dev model takes users and business to places the initiative didn't want them to end up.  Whether it's Google's centralized services or Apple and Android smartphones that spy on the user, you can't fight back if you aren't willing to state the fundamental principle that users must be free to determine how the devices they own actually operate.

If anyone wants to read a principled statement on user freedom, it's here:
http://www.gnu.org/philosophy/free-sw.html

-Jonathan