You're entitled to your opinion, but that seems a bit speculative to me.
FAXstf failed and you're assuming that it has to be because there is no market. Plus, the failure can't be down to inappropriate marketing because you didn't personally observe any particular marketing deficiencies?
eFax and it's various competitors clearly illustrate that the market for a soft fax exists. One plausible reason why nobody has yet taken on the mantle left by FAXstf is that an online service is the dominant business model. Or, maybe, OS X software developers are simply turned on by sexier apps (fax is kinda past it's prime). Or various other reasons.
As for Smith Micro... They've tried to establish themselves in every market place from games to business tools with limited success, and the established brands (eg. Poser) that they acquired, they've only managed to make more obscure. They failed to position themselves as market leaders in any of their chosen corners of the software industry, despite being around for quite a long. All things considered, I imagine they have an intimate knowledge of marketing deficiencies.
It's an interesting debate, but I don't want to get entangled in whether the software should or could exist. I was just enquiring to see if it does exist because I simply want to receive a fax.