I liked your post mate - but Im not too sure about this.
I think it is better to have men on both posts.
I think Ive seen on a very regular basis, men on the post clearing off the line at corners.
Re your point about offside, it seems to be flawed.
Surely you are talking about a one yard at best advantage here? Normally you will have an
opposing player right by the goalie anyway, and others about 1 yard from the goal line.
If the ball is cleared, these men on the post should know to get the hell out for the offside
only when the ball is cleared a long way.
But what if the ball is not cleared out of the box? or just to the edge? You dont want to be thinking about
offside then - you want your men to stay at the post in case the ball comes goalwards.
OK, first things first.
Yes, we see those players clearing the ball regularly. What we DON'T see is how many times that header wouldn't have happened if those players had been attacking the ball instead of stood there on the post. Remember - those post players do absolutely nothing unless the ball actually goes right at them, which yes, it does quite often, but round again and how much less would the ball get to them if they were trying to win the header in the first place?
Then, we also don't see how many breaks that team would have from corners without the man on the post. Sure Cole's cleared a few, but how many goals have Chelsea missed by not hiving him in a position to break at speed when they get the ball back?
As for that second goal - I don't have any figures or whatever to hand, but I've seen it loads of times. Watch MOTD for a couple of weeks with that in mind - you'll see a lot of goal mouth scrambles/balls played back in where it is indeed the men on the post keeping the eventual goalscorer on-side, either because one or both switch off (which happens a lot because also it makes more sense to put non-defenders there, precisely because defenders tend to be needed in a more pro-active role), or because they physically can't make up even that 5 yards of space in the time it takes for the ball to come out and then be played back in - bearing in mind that the defensive line is moving forward at the same rate as the full-backs, so that 5 yard space just shifts up the pitch as the defenders do - again, watch teams on corners and you'll see that decent strikers nearly always occupy exactly that space between the advancing defending line and the full-backs behind them.
So, what if the ball is cleared to the edge of the box?
Again, yes the players on the post can stop that shot when it comes back in, but again that leaves two less players potentially in a position to close down that shot in the first place, or even better get there as the ball is cleared to the edge and set us up for a counter attack, which we do a LOT, especially when the ball is cleared to the exact area you describe.