The modems are covered by import/export controls, which the government has much tighter control over than software, which is effectively speech (at least today)

The modems are covered by import/export controls, which the government has much tighter control over than software, which is effectively speech (at least today). Past attempts to apply those controls to algorithms, cryptography being exhibit A, haven't worked. It is an interesting question if there's a good way to produce a legal vehicle to apply import/export restrictions to software, but this definitely isn't it.