That's true. I haven't been able to find out what the threshold is exactly but I read it's somewhere between $10-40.
But the SEO value isn't just in the links if you manage to get free traffic from them. People can follow the links, it's just that the SEO goodness of STeemit won't flow through the link if it's no follow. But the posts themselves are indexed and found online by searchers.
So it all depends on your objective - drive traffic or to raise the SEO ranking of the destination website.