Inventory Turnover - An Alternative

I was thinking about Inventory Turnover (and other similar accounts and operating / activity ratios) when I noticed what I thought were some assumptions that were made that might not be appropriate for all business types.

Recall: The formula for Inventory Turnover is: COGS / Average Inventory

For intance, if you look at an annual report this is what you see regarding inventory:
You get only two numbers regarding the ending balance last year (beginning balance this year) and the ending balance this year. The assumption is that the inventory gradually increased from it's last year's value to this year's value. So we take the value of the area under the graph to produce an average Inventory (Area divided by time).
Rather than calculate the area under the graph of an awkward trapezoid, an easy way to do this is to approximate the volume by taking the average of the two points and taking the area of the resulting rectangle (assuming the line above is straight, this is an exact approximation).
However, while this assumption might be a good approximation for most businesses, this inventory model isn't appropriate for many other types of businesses. Which kinds? I would argue businesses where design is important the inventory takes a much different shape (as shown below):Which types of business might exhibit this behaviour? I would suggest two candidates would be clothing stores or automotive dealers. Why? Because they often shift their inventory for new models every year. Their inventory levels will spike starting at the beginning of the year and then towards the end they will sell out all their inventory to reduce carrying costs and get rid of "old" inventory which will be harder to sell (or sell at a discount etc).

The point I'm trying to make is that if you use the previous (generally accepted) model, you will be underestimating your inventory turnover model because your ending reported inventory is not an accurate reflection of your "average" inventory carried throughout the year.

In the same way some people might cheat a stock price by invoking a "window dressing" price (deliberately bidding up the last trade of the day to inflate the close, I think that if you aren't aware of how the inventory moves throughout the year, you might be in danger of accepting a "window dressing" inventory value.