The point is that Native Client binaries are arch-specific. You only get the archs that you build for: If someone puts up a NaCl site with only x86, it won't work anywhere else. This is a horrible thing for the web.

Yes, you can build for more than one arch. But if you have x86 and x86_64, you are missing ARM. If you add ARM, you are missing PowerPC (consoles) and MIPS (some phones). If you add those, you are still missing new archs that will be invented later.

For this reason Google is working on PNaCl - but it has other issues.

You need to make it work for it. It's not a very good analogy because parts are portable, but good enough for me: I can recompile my C program for arm. Doesn't make the x86 binary run.

Opera is funded by search deals, but I think I read that they make most of their money from carriers in return for installing Opera Mobile on phones. Not 100% sure though.

In any case, Opera has always been one of the biggest supporters of the open web, through working on standards, opposing things that are bad for the web, etc.

My concern is for content increasingly being siloed within an app that only permits its use in ways encouraged by the author. An IDE is a decent counter-example, since nothing like it would have been feasible before js apps began displacing the web. But it's more and more unlikely that any app other than that IDE will be able to access your source code, simply because it's easier not to bother supporting a stable and documented API when the maintainer's favored client can be revved at a moment's notice.

Yes. Which means it does NOT run on PPC, or MIPS, or IA-32, or Sparc. Note that there are modern-ish web browsers available for at least PPC, MIPS, and Sparc.

More importantly, content using NaCl would not run on any new hardware platforms that might appear.

So if the web were to use NaCl to an appreciable extent, new platforms would be unable to get any traction in any context that relied on the web. We'd be stuck with ARM or X86 forever for any mobile devices we might have.

Maybe you think that's ok; I think that's a terrible idea; an attitude like that toward the web in the late 1990s would have meant that ARM phones that appeared in the late 2000s would not have been able to browse the web!

(Also, note that I said "hardware _platforms_", not what you asked above.)