So if 20 million Macs are sold worldwide.
40% in the US = 8 million Macs
25% of Mac sales = Mac Book Pro 13 inch (exclude iMac, Mac Book Air, Mac Pro, Mac Book Pro 16) = 2 million Mac Book Pro 13"
If only 1% of that figure were broken, that would amount to 20,000 overheating models
If 60% of customers are willing to put up with this heating, the remaining 40% = 8,000
If 90% of these 8,000 look elsewhere for solutions (Genius Bar, other forums) or just read this forum without posting, the remaining 10% is just 800 people posting in this thread and other Apple Discussion threads.
That is not impossible to imagine when including other Apple Discussion threads on the same topic over time; I remember such a number for GPS issues on the iPhone.
These assumptions are just very very very rough guesses, but I hope you get my drift: The number that show up with reports of issues in these Apple Discussion threads is WAY smaller than the real number of Macs with problems.
On the other hand, 1% would be a low risk for some buyers. But MacBook Pros aren't cheap - it is a lot of money to waste on a product you are not happy with.