The developers don't have a choice. Bitcoin uses strong cryptography, which, for reasons which don't really make sense, is legally classified as a military weapon under the Wassenaar Arrangement, and therefore illegal to export to "certain" countries. Simply making the source code available for download worldwide is legally equivilant to selling bombs to Iran. As fucked up as the law is, it must be obeyed if you want to avoid being jailed for arms trafficking.
This is not true. Open source, free software does not fall under the US munitions export controls. Otherwise, tools like openssl, tor, openssh, linux distributions, etc would not be available outside the US. See
https://www.federalregister.gov/articles/2011/01/07/2010-32803/publicly-available-mass-market-encryption-software-and-other-specified-publicly-available-encryption for the public restatement of that fact. This fact has been true since 1996. See John Gilmore's fights and wins in the US courts here,
http://www.toad.com/gnu/export/export.html.
My understanding was that SourceForge is claiming that the specific OFAC sanctions against Iran would take precedence over the munitions export controls which were indeed relaxed for non-sanctioned countries. It just hasn't been challenged yet.