It was interesting. I rang Apple, and the guy got me to hold on while he checked other rMBPs. He came back and said they all did it. I didn't really believe this, since mine was intermittent, and maybe dependent on the battery charge at the time. I let the whole thing go. It wasn't that big a deal . If the light didn't come on, I could usually remove and reseat the Magsafe adapter and things would be fine,
And then a couple of weeks later, I got a call out of the blue from Apple saying they wanted to "capture" my machine for further anaylsis, and that if I was OK with that they would send me a new machine. They even let me keep the old one until the new one arrived (with a credit card guarantee), then I sent the old one back. So obviously this must have been a known issue.
And the new one? Still has the same intermittent problem! Doesn't really seem to affect anything though. I let my email contact at Apple know this, but didn't get any further feedback.
Is yours intermittent too? Sometimes the light does come on straight away and sometimes not?