Those are four huge names. If they were caught, this would be due to testing last year. Maybe the offseason, but I'd doubt it for all four. A lot of people would know, from multiple teams. Braun's 2011 test, which ocurred in October of that year, was reported on in December 2011. I can't see that these names were sat on for 5 months.
Cano and the Yankees are supposedly close to announcing a huge contract extension. No way they'd be talking if this was about to blow up in the news.
As for PED use in baseball -- MLB does more testing, plain and simple. Compared with football, the season is much longer, which creates more opportunities for tests. I'd be surprised if usage rates differed much across most sports, so the more you test, the more you catch.