Here I am with you 100%, wagering sites should not allow ambiguous bets, players should also not be placing wagers on ambiguous bets either. Betsofbitco.in is also in a similair position for allowing an ambiguous bet to be placed then nullifying it later due to being ambigious.
Neither bet was ambiguous at the time it was allowed. The only thing that changed is that BFL found yet another way to scam. Betsofbitco.in empowered this scam (which comes as little surprise, they were in BFL's pocket anyway, as detailed other places on this forum). BitBet did not.
If tomorrow somebody makes a bet saying "Ford will deliver most 2014 Ford Fiesta preorders during 2014. Product must meet advertised performance to qualify as delivered." it will be accepted, as it's not ambiguous. In sane everyday reality Ford will do exactly that, or else issue a statement explaining they've canceled the series/failed delivery/production/whatever. If Ford were to come up with an announcement saying the 2014 Ford Fiesta is now a Husqvarna lawnmower from 2007, refurbished, then we'd be in BFL scamland.
The reason Ford doesn't do this sort of crap is simply that Ford is a company, not a scam. The reason BFL does do this sort of crap is simply that BFL is a scam, not a company. It is impractical to go around specifying everything a scammer may in time change. For instance, no delivery bet contains a rider saying that "should the product delivered have a long rubber hose affixed transforming it into a YoYo then delivery is invalid". This does not make the bet ambiguous, and even should BFL add rubberbands to their products and try to foist them from the customers' hands later the bet still wouldn't be "ambiguous". BFL would be scammy. That is all.