One of the best criticisms of an article in @Quillette I have yet seen. On the (de)merits of the content (credibly argued as flawed and possibly biased, with evidence, not insult). This is how intellectual criticism should be done.http://ow.ly/5dJw50tSPS8
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That's a different argument than your parallel lines one. Sample size argument depends on what effect sizes you expect to find. They had enough to find a massive difference (d > 1.00), like often seemingly claimed. They didn't have enough to find d = 0.30 or whatever.
The lines are not based on data in each group, it's from the model fit, which assumes no interactions, hence lines must be parallel no matter the amount of data used to fit.