No, there's nothing unethical about that at all. In fact, it's a quite common approach. For a long time, it was actually very uncommon for many "commercial OSS"

No, there's nothing unethical about that at all. In fact, it's a quite common approach. For a long time, it was actually very uncommon for many "commercial OSS" projects to release binaries that you didn't have to pay for... JBoss were one of the first major players I recall doing that early on. Anyway, if the code is open and developed in the open, and they have the ability to build from source if they want, then nobody really has any standing to call you unethical for not providing tested builds for free.