I can explain how our retroactive tool works, and what the intent is.
The intent was always to provide an option to leagues that don't quite get themselves ready to roll by opening day. The way it works is that there is a commissioner setting for the "retroactive date". If the commissioner sets that date, then when that date arrives, the starting lineups for each team are noted, and the league scoring is calculated from scratch as if the teams had been using those starting lineups since opening day.
If you started a week late, and just want to associate some value with the first week of the season, this is a reasonable approximation. If you are well in, have been making drops and adds, trading, whatever, then it starts to become a pretty pale substitute for actually playing the game for the missed time. But it is an option; if you decide it is better than nothing you can use it, or you can choose not to.
As for the usability of Yahoo's site, I can only say it is staggeringly good
Not that I'm biased or anything.
Hope this helps...