Gawker,to answer your question. Physical attrraction is possible with anyone whether you actual work with them or not. That does not itself mean much. Ofcourse if you are working close to that person, the attraction can be stronger than if you admire that person from a distance.
But then again as Poo mentioned these people do not do the scenes in continuity or in privacy. With atleast ten people watching your every move, I think shooting for intimate scenes must be the most difficult for any couple, more so if they are really seeing each other and do not want the rest of the world to know it yet.
Many onscreen couples become off-screen pairs not only because they work in intimate scenes together. I think their relationship builds over the time they spend with each other off the screen. You see these actors have to put in long hours of work,like 10-12 hours everyday and sometimes even mroe. So they may be constantly thrown in each other's company which may lead to their getting to know each other better. If they like what they learn about each other, their relationship may take root. Otherwise it may just be a fling.
Agree with Tweety that physical attraction is not the only thing that matters in a relationship. there is much more to an individual than his/her looks. Two people who may look the most attractive on screen may be totally mismatched in character. Such couple may never be drawn to each other even if they are constantly working together. It is hard to put a finger to it and say, yes this is what will work in a relationship. And as outsiders, we certainly have no knowledge of anything to conclude anything about Shachi or any other pair.