The powers-that-be at WMGK couldn’t have made a more prescient move in hiring John DeBella and Debbi Calton, both much-loved castoffs from WMMR, now MGK’s younger, edgier sister station in the expanding Greater Media empire. Big surprise: Many of those who grew up listening to MMR followed those familiar voices to a new frequency. Since then, MGK has capitalized on its baby-boomer niche, playing it safe with a core playlist of untouchable artists like Tom Petty, the Beatles, the Rolling Stones, Bruce Springsteen and the Eagles. Never underestimate the power of familiarity.