In my opinion the main reason that questions like "which size TV did you want to go with" force them to say either "no" or commit to moving forward. It is amazing how often we, as salesmen, walk away from a sales call without ever actually asking for the customer's business. If you rewound some of your sales calls in your head I bet that you would find that it would be difficult for the customer to find a time in the conversation that you actually invited the customer to move forward.

We pitch our product and ourselves, but then we back away from the conversation and give them time to think about it. If we did a good job they will never be more ready to commit than at the end of that conversation. Allowing them time to think only breeds new distractions and chances for competition. Unless you did a good job selling against the half-truths that the next CI that comes along will tell ("I don't think their system does that.") then that guy is now in a much better position to close that sale.