Plenty of things have been retconned in comics over the years, some smartly, others clumsily.

Beyond the Clone mess, there was the failed attempts to combine all the Hawkmen, the incomprehensible and conflicting storylines of Wonder Girl, Donna Troy, Power Girl and about 17 Supergirls. The Green Lantern he-blew-up-Coast-City wait no he didn't. The disappearance of Scarlet Witch and Vision children.

The disappearance of Spidey and Mary Jane's daughter. The death of Auny May in issue #400, but wait. She was a clone, too. The stupid revelation that the Human Torch was never married to Alicia -- she was a Skrull -- after several years of that storyline, and the reappearnace of Skrulls now in the Marvel Universe and they can be any hero at all.

Redoing a character is common -- the Ultimate line, the Crisis and revamping of Superman, Batman and Wonder Woman. Removing Wonder Woman from the JLA and saying it was Black Canary and not WW.

But this Spider-Man development may top them all for sheer wish-it-all-away remaking of a character. I actually think it was handled pretty well, but it's pretty mind-numbing, especially after Civil War and now, well...