I ride chicago streets and was 259lbs at one point. im at 239 now on 23c and so far so "knock on wood". I wouldnt think that it would be an issue unless your bunny hopping curbs and such.
i wonder if the wheel and spokes were bad? i got a new wheel last year and the kid didnt put any rim strips so the spoke were poking holes and the wheel went out of true in a month. took it back and the owner fixed it all up for me and it went all summer/fall strong.
its not you or your girth just a bad wheel i think.