> Judging by the increase in sales year over year for the Macbooks...
...you get a number that tracks the economy in general and the consumption of luxury electronics in particular, is affected by the relative strength of Apple's ecosystem against Microsoft and Google, how badly Superfish has affected Lenovo's reputation, etc. etc.
And in any event the numbers aren't particularly optimistic:
http://blogs.wsj.com/digits/2015/10/08/apple-mac-sales-slow-...
> How many sales has Apple gained by making the laptop thinner and lighter and giving it a longer battery life compared to sales lost from not making a few parts user-replaceable?
We don't even have all the data yet. Customers don't realize they want a user-serviceable battery until they've had to replace one that isn't. Apple started selling glued batteries three years ago, which means they're only starting to have to be replaced now and the largest effect will be seen going forward when the people affected are buying new laptops.
But you're asking the wrong question anyway. The interesting question is: What would their sales look like if they had both ultra lightweight models and slightly heavier models with user-serviceable parts?