I think this hardcore attitude about showing up to every session may be one of the leading contributing factors to the decline of roleplaying as a hobby. How can newer players get into a game once it transcends being simply a game and becomes a hard commitment? Guys, it's a game, and we're talking about it like it's a budget meeting or something. We're all grown-ups and things come up. I've missed gaming sessions just because I was too tired to play, and I don't think there's anything wrong with that. No actual negative consequences will result from me missing a game. The game will be different that night, but that's it.
That being said, I've never been a habitual absentee from gaming, and I usually motion to drop habitual absentees from my gaming groups. There's a line between "life happens" and "I'll show up for about half the games if I feel like it." Sometimes, though, life happens at the last second.
Here's the way I do it. If someone doesn't show up to a session that all have already committed to, we have an understanding that their character will be played by another player. The receive no karma for the run, their characters cannot use edge for any reason in their absence (just started this one, but it hasn't come up yet), and if they die they die. That's incentive enough. We don't need to concoct an appropriate punishment, rationalize a PC's absence in mid-run, fill a role left vacant by a missing player, etc. The best part is that the game goes on as scheduled, and the negative effects on the other players are minimized. Isn't that the whole idea? This solution works to solve the problem created by the absent player rather than to seek retribution for the problem that was created (for deterrent purposes or otherwise). Plus, there is a deterrent effect to not controlling your own character (especially if edge is out). It's not like they're skipping out on babysitting your kids or something. They just didn't come to game night. Now sure, if it's a regular thing, then the PC will not be joining the next run and you can start looking for a new player.
I don't think we can talk about respecting schedules if we are going to demand explanations for absences, and impose punishments if said explanations are found to be inadequate. Tell them when the game is, let them know that if they don't show up their character is in the same danger with no chance for a karma reward, and play the game.