Granted, Pulley is about 20 years older than Andre Royo's "Bubbs" character, but that's kind of the point. Imagine if Bubbs had stayed on the streets for the rest of his days...
He'd probably still be getting beaten down for his pocket change by crooks and drug dealers and trying to protect himself in the only way the streets know how (i.e. without help from the police.)
Now, the real-life backstories of Johnnie Pulley and his victim Brandon Colenburg have yet to emerge, so any comparisons are pure, unadulterated speculation.
But still, it's not hard to imagine Pulley as a sympathetic and flawed character like Bubbles, doing his best to get by on the mean streets of the Northside. He says the teenage Colenburg previously assaulted him (a claim police could not verify because Colenburg died before telling his side of the story), and Pulley was either exacting revenge or defending himself from another beating when he pulled the trigger.
Yup, yet another reason why The Wire is the greatest show in the history of television. It's just so...Dickensian.