I believe a better question is: Why can't this problem be solved in hardware? So, it won't depend on the OS and if I shutdown my laptop and leave it on the charger it will still work.

My 3.5 year old Asus laptop has still similar battery life as it had when it was new. I always keep it on the charger when I can and sometimes I just shut it down and leave it on the charger overnight too (but this is rare). When I bought it, I have noticed that the battery was never above ~95%, but I have never studied how it works exactly (is it done by HW or by the driver). I have used it with Win7, Win8, Win8.1 and now Win10.

Thinkpads (used to, don't know about these days) ship with a utility that allowed to prolong the lifetime of the battery by limiting the amount it will be charged. The article mentions "tlp" software which apparently does similar thing. So yes, it can be solved in software.