[sciurus]

OpenSSL's license imposes additional restrictions which are not compatible with the GPL. Thus, if you release code under the GPL but want to allow people to link it with OpenSSL, you need to provide an exception.

There's an article covering the topic with much more nuance at https://lwn.net/Articles/428111/

[Intermernet]

Thanks, I had originally thought it may have been some residual effect of the export embargo on crypto (http://en.wikipedia.org/wiki/Export_of_cryptography_in_the_U...;

I'm going to have to do some more reading on this. I was particularly interested in the quote "the problem here is actually a former OpenSSL hacker who has no interest (and, in fact, a positive interest against) in changing the OpenSSL licensing". Sounds intriguing!