Maybe I am just cynical, but I think the companies would rather make something that is going to run a little too hot and wear out faster so that they can sell you a new one sooner.
I don't think you're cynical. However, I think that in order to deal effectively with heat they'd have to install more expensive components/spend much more on R&D, so the cost to the consumer would go up. A lot. So, in terms of consumer perceptions, they're damned if they do, damned if they don't, but win either way! That is, if they spend the R&D $$ and install pricier parts, they can charge more BUT consumers will moan and complain about costs. If they don't bother, costs are down, consumers are happy with the supply of cheap notebooks BUT they moan about heat dissipation issues and short-lived notebooks... However, in a hypothetical world where ALL notebook manufacturers spend the same R&D $$ and install the same level-of-quality components, they collectively either make money selling new notebooks to repeat customers every 18 months OR they make money on higher purchase costs to consumers. Add in the fact that s/w, O/S's, and hardware keep advancing and there is a market for new equipment either way... Ramble, ramble, ramble