It may seem like a small thing, but speaking as a scholar of the period, there's a world of difference between the two. Lemme see if I can offer a comparison:
Johnny Rotten is to Sid Vicious as Kevin Smith is to Jason Mewes.
John had very specific ideas about music, fashion, and society which he expressed through his style and lyrics despite a complete lack of vocal talent and formal education. For a brief shining period, he was able to embody the fear and loathing of a society that was collapsing upon itself. One 19-year-old kid became England's Public Enemy Number One through his lyrics, attitude, and grooming. Not since Elvis has a pop musician had such a dramatic effect in such a short time. Post-breakup, he alone had the foresight to retain the rights to his music, and the brains and balls to fight for what was rightfully his (it took 15 years, but he won). And, post-Pistols, he had a respectable career fronting PiL.
Sid Vicious was a deeply damaged man-child who was completely unable to cope with success on any level. He couldn't play, had no ideas, and no emotional defenses to protect him from the demands of fame and stresses of infamy. Fun fact: on the Sex Pistols' one album, all Sid's bass lines are overdubbed by Glen Matlock. Sid was brought into the Pistols because of his attitude, not for anything resembling talent. He was a nasty, brutish gutter punk who became the worst rock-and-roll casualty of all time.
"What do I want? I'm an American. I want more."