Maybe he just forgot about it. I mean, maybe Clemens scheduled his appearance at the charity event that bares his name (Johnny & the Rocket Swing Fore Charity) during the second week in October and just plain forgot that the ALCS is also scheduled during that time. The guy is old afterall. Or maybe this was all part of his "Clemens Old Person Family Plan" with the Yanks that allows him to skip starts in the playoffs or not be with the team during the first couple games of the ALCS because he's gotta swing the wrenches with Johnny Bench and Jay Haas (Haasticles won the event last year). Or maybe because he wasn't going to start a game for the Yanks until games 3 or 4 anyway, he just figured he didn't need to be around for games 1 & 2. Or maybe old people have the ability to see the future and because of that he knew the Yanks weren't going to make the ALCS. Or maybe Clemens is just a dick and scheduled his charity event during the ALCS because he's doesn't give a fuck about his team.
Who knows why he did it and it didn't end up making a shit of difference because the Yanks are out of the playoffs anyway. But this could have been a big deal for the Yanks if they were still in this thing and they'd have to deal with it in the media. Or maybe the Yanks would just have bent over and taken it from Clemens in this situation like they have every other time.