Not always. Higher sales have stopped indicating the best product a long time ago in Western consumerism and marketing. Take virtually any unrelated product and you'll rarely find that experts or enthusiasts rarely use the best selling brand names and opt for higher quality niche manufacturers. Your car analogy works very well here. North American brands like Chevrolet almost every year have a car that was "The top selling brand of 2012!". But compared to numerous imports, the car sucks. I'd like to see the return rates on the S4 because I've seen significantly more grumbling about the S4 than the One on carrier customer reviews after the sale
Your post defies logic and ignores consumer buying habits. The S4 sales numbers are for worldwide sales and the manufacture is a Korean company. How does Western consumerism explain that? By your own statement a company targeting experts and enthusiasts would have small sales figures. Do you think experts and enthusiasts are being targeted by other high end smartphone manufactures? Of course not, they are mainly targeting the average consumer. But even experts enthusiasts are buying the S4 if you believe the posts on this and other enthusiasts sites. You also overlooked the millions of sales of the S3. The S4 sales don't exist in a vacuum. Those who bought the S3 obviously aren't filing class action law suits or filling news print space with complaints about problems they had with the S3. They are making recommendations to their family and friends on which cell phone to buy or are upgrading to the S4 themselves. In reality the only articles I have seen posted about a high numbers of returned phones are regarding the HTC One. If you have seen an article about a large number of returned S4s please post a reference.
"I've seen significantly more grumbling about the S4 than the One on carrier customer reviews after the sale"
Would you please provide a reference or web site for that information.