Are there particular platforms you're thinking of? The big complaint was iOS, which was resolved a while ago. (The legal constraints around the app store are complicated, but basically, Apple does not reject GPL apps. So it merely requires the copyright holders to agree that distribution on the App Store does not infringe their rights under the GPL, which is a reasonable position to take.)
For a library that is GPL, you would need that library's authors to relicense it to allow it on the App Store.
It's not that reasonable: the Apple EULA requires things that directly conflict with the GPL, such as the EULA requiring non-distribution of the binary.
Many paranoid companies will often prohibit all use of GPLv3 software. The justification I've heard is that the terms of the license make it possible that anything you produce using GPLv3 software is also GPLv3. So, for example, if you use a GPLv3 licensed version of emacs, and you write some code, the code you wrote will also become GPLv3. It's a very conservative reading of the terms of the license, but understandable for companies which have most of their net worth tied up in source code.
I forgot to point out while the discussion was still active that "proprietary encryption" is a bit of a misnomer. 90% of people who use that phrase mean "we use a super-secret algorithm and if we tell you how the algorithm works the bad guys will break it", aka, a weak and unaudited security-by-obscurity algorithm.
OCB is no more proprietary than RSA was when it was still under patent protection (throughout the '90s, I believe), the reference implementation is public, and Mosh incorporates the reference implementation into its GPL source. The algorithm is well-documented in the research literature, and the implementation is available under a free software (though strong copyleft) license.
Because depending on the policies of your workplace, GPLv3 may be blacklisted; the nature of that license makes its use in certain classes of business very, very dangerous.
Many paranoid companies will often prohibit all use of GPLv3 software. The justification I've heard is that the terms of the license make it possible that anything you produce using GPLv3 software is also GPLv3. So, for example, if you use a GPLv3 licensed version of emacs, and you write some code, the code you wrote will also become GPLv3. It's a very conservative reading of the terms of the license, but understandable for companies which have most of their net worth tied up in source code.
It's not a conservative reading so much as an incorrect one, and it's also nothing to do with v3 versus v2. The concern about v3 is that it means that companies are not allowed to use patent or hardware restrictions to do an end-run around the GPL's user protections.
The "viral contamination" FUD has been around for over a decade at least; it's nothing to do with version 3.
This shows a bit of a misunderstanding of how copyright law works. Just because a tool was used in creating a work does not mean that the created work is a derivative, unless the work somehow incorporates the tool.
