I often heard myself that beer itself can be considered an isotonic drink.
I quote some interesting parts of this Royal Society of Chemistry's article, maybe the studies the DailyMail talks about are those linked at the bottom.
[Beers] high water content more than compensates for its dehydrating effects.
One other fact about beer that may come as a surprise is its fairly high content of protein and vitamins. Beer contains about 2 g of protein […] nearly 4 g per pint of water-soluble B vitamins: rich in niacin, pantothenic acid, pyridoxine and riboflavin, beer is relatively low in only two B vitamins, thiamin and biotin.
One of the other benefits of drinking beer is that unlike some other drinks, it contains relatively low levels of sodium. Typically, the Na : K ratio is just 1 : 4, compared with a ratio of 29 : 1 for some sports drinks.
If you worry that alcohol prevents recovery of muscle, there are studies that show that high alcohol consumption actually does.
consumption of [a beverage containing 1 g of ethanol per kg bodyweight ethanol] after damaging exercise magnifies the loss of force associated with strenuous eccentric exercise.
But smaller amounts don't.
consumption of [a beverage containing 0.5 g of alcohol per kg bodyweight] after damaging exercise appears to have no effect on the loss of force associated with strenuous eccentric exercise.
If you drink 500ml of beer, which normally has around 5-8% of alcohol, this is around 25g-40g of ethanol. This amount is at or below the value of the second study, depending on your body weight of course.
There are of course very different types of beer and by that its contents will vary. Additionally alcohol-free beer exists that doesn't bring the downsides normal beer does, but it still brings the benefits. Some alcohol-free beers are actually marketed as isotonic in Germany.
As an anecdote: The Vattenfall Cyclassics, an annual bike race in Hamburg, has Erdinger (a beer brewery from Bavaria) as a sponsor, and both alcohol-free and normal Erdinger Weissbier is well received after the race both by the crowd and the racers.