at even a litre a day he is drinking more than the body can get rid of
even if your body build up a tolerance, the tolerance can only go so far, for example
unless your uncle is severely overweight i doubt he drinks a litre every single day because he would have to take a rest at least once a week for the body to lose the alcohol thats always building up
I've seen some who drink 2 bottles a day.
There are several "myths" here. Yes, tolerance can only go so far. Tolerance in this case is neuronal tolerance for blood ethanol concentration (brain).
Dont also forget that your kidneys are also able to excrete ethanol, since it is water soluble, and isnt actively re-absorbed by the distal/collecting tubules, and is peed out.
So, what happens in alcoholics is that they run a very high ethanol level, which their brain can survive but not yours, and that is excreted both by the liver and kidneys, over the course of the day. So while it might not kill them, it would almost certainly kill you. Different peoples brain have different tolerances, which we see in different peoples ability to "hold their drink".
After a while, their liver gets more and more "pickled". So their ethanol metabolism goes down. But their kidney excretion will increase as it is linked to blood ethanol concentration (which is going up), but it wont be able to keep up. As with all things, there is a limit to how high it can go before your brain cant take it. So after awhile, you see alcoholics alcohol intake DROP, because they get well drunk after a small amount, largely due to the fact they cannot metabolize much of it. By then they are usually a tinge of yellow, with gross ascites, have deranged clotting, oesophageal varices.... etc...