There's only one problem with this open letter: the wrong companies are making this request.
Here's the reason why: many suspect that the NSA has tapped directly into the Internet backbone lines owned by the likes of AT&T, Level 3, Sprint and Verizon. As such, they are essentially "scooping up" all the Internet traffic without having to access the servers at AOL, Apple, Facebook, Google, Linkedin, Microsoft and Twitter and using NSA's gigantic complex of supercomputers to analyze all the data. Now, if the Internet backbone companies were signatories to this request, THEN I'll take this letter much more seriously.
You make an excellent point. All of these companies say they don't allow "Direct" access to their servers...that definitely leaves out "Indirect" access. Take Apple for example. They don't even have/run all of their own servers...they outsource it to Microsoft Azure and Amazon servers, among others.