It is not law that caps the definition of beer - it is the fermentation process.
Both beer and wine are made by yeast fermenting sugar. (I've homemade both.) In every case, as the alcohol level in the batch rises it reach a level(depending mainly on the strain of yeast and temperature) that kills the yeast and you can't get the beer or wine any stronger. That level is never very high - anywhere from single digits to 14-15%.
To take the batch beyond that, to a higher alcohol content, you must distill or fortify it something other than true beer or wine. (Examples: brandies, ports, sherries, liquors,etc.)
IIRC, BrewDog in Scotland used a freezing process to force water out of the brew and raise the ABV. I suppose that's a type of distilling.