It's a nice way of showing consumer excitement for your product and tells you more about what people are actually buying than shipments. You're definitely right about that. It's not like I'm saying that it's not a much more "down to earth" way of reporting sales.
But when it's not a traditional metric (and when the reporting of traditional metrics has been watered down), there's no good way (for us laymen who don't have all the internal estimates) to use it to make comparisons (which are necessary for identifying long-term trends).
I'm struggling to understand your perspective on sell-through figures. There is not a single consumer goods company in the world that does not rely on sold-through numbers to establish internal goals and analyze market needs + trends. If such a company does exist, then that company is the luckiest company in the world, or that company will be dead in the near future.
Sell-through numbers are the most accurate sales data that a company, analyst, or layman can utilize to determine the past, present, and future adoption of a product. You cannot sustain high shipments of products if people aren't actually buying your products. It's really that simple. If you're trying to figure out long-term trends for your product, you need to figure out current market trends, and you can't successfully do this without knowing how many people have your product.
For example, let's say Under Armour is trying to figure out what will be fashionable in basketball footwear, in 2016 and 2017. Let's say they're specifically trying to figure out what the next Steph Curry shoe should 'be'. Under Armour will need to know about 15 key things about the current Steph Curry shoe and the marketplace:
1) How many people bought it
2) How much money they make per sale (and how much it costs to make the shoe)
3) What features on the shoe are marketable (i.e. attractive)
4) How people use the shoe (e.g. Indoor play or outdoor play, casual wear or athletic wear)
5) What retailers and consumers say about the shoe
6) Who's wearing the shoe (e.g. Race/ethnicity, gender, age, income level, education level)
7) What people wear with the shoe (e.g. Fitbit, basketball jerseys, armbands)
8) What's the popular alternative to the shoe (e.g. Lebrons, KDs)
9) What retailers and consumers say about the alternative(s)
10) Who's wearing the alternatives (e.g. is it the same people who wear the Steph Curry shoes?)
11) How much do the alternatives cost
12) Where did they sell the most amount of shoes (e.g. California)
13) Where did they sell the least amount of shoes (e.g. Ohio)
14) What other products do people who bought the Curry's own and plan/indicate to buy (e.g. iPhones, PS4's, Patti Labelle pies)
15) When did people buy the most shoes (e.g. month/season)
These are a few things that Under Armour would need to know before they can identify realistic long-term trends. Consumer satisfaction, product recommendations, consumer perception, product pricing (and comparative pricing), product mentions, product usage (aka what are people actually using the product for), time spent with product, product associations (aka what do people relate the product with), product life cycle (PLC and relevant S curves), etc. All of these are relevant.
None of these, however, are more relevant than product sell-through. This is why we can look at the videogame industry -- specifically, the console business -- and identify future trends. For example, we can identify which console will be supported the most and have the most content in 2016 and beyond. We can say that unless Microsoft and Nintendo start handing out blank checks, more and more publishers and independent developers will align their future games with the PlayStation 4. Why? Because the PlayStation 4
sales-figures in major and minor markets are significantly higher than the sales-figures of the immediate (Xbox One) and future (NX) competition.