Moreover, even if only the 10% best informed people use PRISM-proof communications, it's a safe bet that NSA's alleged targets (whatever the current definition of "terrorist" might be) are among them, so the argument that they're doing that to catch "terrorists" doesn't hold water anymore.
I believe the tech community is concerned about this, because it threatens the robustness of Internet. Today, nobody in the business can pretend with a straight face that top-level certification authorities are trustworthy; so I expect the next generation of security protocols, the successors of the (transparent and enabled by default) SSL, to treat governments as opponents.
I also believe that companies will change their security patterns, e.g. stop trusting American third parties such as Microsoft if they have competitors with political connections in Washington.
I agree with you, but I think you have far too much faith in ordinary Americans. I invented some widely used anti-phishing technology, and I can tell you that spending a few months analyzing actual incidents where otherwise intelligent people did ridiculously unsafe things on the Internet will give you a new perspective on the tech savvy of the general population. Unless we (the tech community) make strong security both transparent to the user and enabled by default, the feds will be seeing everything they do. Sadly, most of them seem OK with that.