When the news broke last night that Robin Gibb had died at age 62, it was sad. But it wasn’t a surprise.

Even though the Bee Gees singer-songwriter had awakened from a coma last month, his doctors warned that advanced colorectal cancer and other health concerns remained a significant challenge.

View Photo Gallery: As part of one of the most successful pop groups of all time, Robin Gibb helped define the disco era.

But that knowledge didn’t change the fact that the passing of Gibb — a man who, alongside brothers Barry and Maurice, dominated the late ’70s pop charts with a string of “Saturday Night Fever” hits and tracks penned for other artists (“Grease,” “Emotion”) — is another upsetting reminder of how much legendary musical loss we’ve seen in 2012.

The alleged rule of celebrity deaths is that they come in threes. This year, the ones that have involved influential figures in the world of pop music have come in droves. Perhaps that’s why last night’s Billboard Music Awards felt less like an awards show and more like one long in memoriam segment.

In recent days alone, we’ve lost two of the most famous faces of the disco era in Gibb and Donna Summer; the father of go-go, Chuck Brown; and Beastie Boy Adam Yauch, one of the key people responsible for bringing hip-hop to the mainstream. Whitney Houston, whose ballads and upbeat top-40 hits were inescapable on the FM dial in the 1980s and early ’90s, passed away in February, the same month that Don Cornelius, host of Soul Train, boarded a choo-choo bound for heaven. Two months after that dance show host’s death, the pioneer of that format and a gentleman responsible for the rating of many records, Dick Clark, died at age 82.

And I haven’t even covered Davy Jones, or Etta James, or Levon Helm, or Jimmy Ellis from another disco-era band, the Trammps, or several other lower-profile but no less appreciated artists who have died before we’ve even hit the halfway point in 2012.

Obviously, celebrities — not to mention regular people — die all the time. But a quick scan of the notable deaths from recent years confirms that it’s somewhat rare to see this many losses in such a short period from one category of the entertainment world.

I’m not suggesting there’s some conspiracy or sense of pre-destiny at work here. The fact that all of these significant musical figures have left this Earth in a pack is a coincidence of timing. But for those whose childhoods unfolded to the tune of their life’s work, it’s a lot to process.

As I wrote shortly after Houston’s death, we often take celebrity deaths personally because their work was, indeed, so personal to us. For those of us who grew up in the 1970s and 1980s, in the eight-track and cassette tape era, we are starting to realize that from now on, more of these high-profile losses will feel especially personal. These people who are dying, the Gibbs, the Summers, the Yauchs and the Houstons, gave us the music that we hear every time we think back to boy-girl parties and roller rink free-skates, to station wagon rides and August days spent soaking in backyard wading pools while the radio blared the staticky sounds of WPGC, Q107 or WAVA.

We knew when Michael Jackson and John Hughes died in 2009 that we were starting to lose the ones that really meant something to us. Three years later, we have to come to terms with the fact that losing the famous artists who defined us is now the new, and very sad, normal.